Mobile node, mobile agent and network system

ABSTRACT

A mobile node moves from a first IP (Internet Protocol) network to a second IP network in a network system in which the first IP network capable of executing communication in accordance with both first and second kinds of IPs and the second IP network capable of executing communication in accordance with only the first kind of IP are connected with each other. When the mobile node communicates a message with other nodes on the first network after its movement accordance with the second kind of IP, a header for the movement containing both home and foreign addresses of the first kind in IP is added to a header containing home and foreign addresses in the second kind of IP, and put to the message, is added. The message to which the movement header is thus added is used for the communication between a first mobile agent on the first network and a second mobile agent on the second network, or between the mobile node and the first mobile agent.

BACKGROUND OF THE INVENTION

This invention relates to a mobile node, a mobile agent and a networksystem. More particularly, this invention relates to a control methodwhich assists the movement of a node between an IP (Internet Protocol)network capable of executing communication in accordance with both IPversion 4 and an IP version 6 and an IP network capable of executingcommunication in accordance with only the IP version 4 or an IP networkcapable of executing communication in accordance with only the IPversion 6, a mobile agent, and a network system for assisting themovement of the node.

With a drastic development of small and light-weight nodes and theInternet, the demand for taking out a node from an office or a home toutilize it everywhere has been increased. When the node is moved toother network in the conventional network environment making use of theTCP/IP (Transmission Control Protocol/Internet Protocol), however,setting of the IP address, which is the information for primarilyidentifying the node in the IP network, must be changed so as to matchwith the foreign or visiting network environment.

Even if this change of setting of the IP address is automatically mae byutilizing a DHCP (Dynamic Host Configuration Protocol) described in RFC(Request For Comment) 1541 as one of the methods of distributingautomatically the IP addresses, there remains the problem that thenetwork connection that has been established already with other nodes byusing the IP addresses used in the network before the movement cannot bemaintained in succession.

Therefore, methods of assisting the movement of the node between thenetworks have been devised. A typical among them is a protocol of thethird layer (network layer) of an OSI (Open Systems Interconnection)reference model and this protocol pertains to the IP version 4(hereinafter called the “IPv4”) that has gained a wide application inthe Internet and the IP version 6 (hereinafter called the “IPv6”) thespecification of which has now been stipulated so as to solve theproblems of address exhaustion in the IPv4. As to these IPv4 and IPv6,“IP Mobility Support in IPv4”) (hereinafter called “Mobile IPv4”)described in RFC2002 and “Mobility Support in IPv6”) (hereinafter called“Mobile IPv6”) described in IETF (Internet Engineering Task Force) draft(the latest version of which is “draft-ietf-mobile-ip-ipv6-02.txt”) areexamples of the known references.

Incidentally, the term “IPv4” used in this specification designates anIP address having an address length of 32 bits while the term “IPv6”designates an IP address having an address length greater than 32 bits.

By making use of these Mobile IPv4 and Mobile IPv6, a user can executecommunication in the same way before the movement of the node even whenthe node is moved to another network, without the necessity for changingthe IP address of the node or cutting off the network connection thathas already been established with other node before the movement.

Incidentally, the term “node” used in this specification designates allthose devices which have an IP address and execute communication byutilizing the IP, such as a PC (Personal Computer), a WS (Work Station),a router, and so forth.

Generally, it is assumed that the movement from the IPv4 to the IPv6 iseffected gradually and all the networks do not utilize at once the IPv6.In the mean time, therefore, there exist a network (hereinafter calledthe “IPv4 network”) comprising only those nodes which executecommunication by utilizing only the IPv4 (hereinafter called the “IPv4nodes”), a network (herein-after called the “IPv6 network”) comprisingonly those nodes which execute communication by utilizing only the IPv6(hereinafter called the “IPv6 node”) and a network (hereinafter calledthe “IPv4/v6 network”) comprising those nodes which executecommunication by utilizing both of IPv4 and IPv6 in mixture (hereinaftercalled the “IPv4/v6 node”), the IPv4 nodes and the Ipv6 nodes.

To beginning with, let's consider the case where the Ipv4/v6 network isthe one that supports both of Mobile IPv4 and Mobile IPv6. In the MobileIPv4, messages are exchanged between a mobile node moving between thenetworks and a mobile agent (hereinafter called the “IPv4 mobile agent”)for assisting the movement of the mobile node which executescommunication by utilizing the IPv4, in accordance with the Mobile IPv4procedures. Similarly, in the Mobile IPv6, messages are exchangedbetween a mobile node moving between the networks and a mobile agent(hereinafter called the “IPv6 mobile agent”) for assisting the movementof the mobile node that executes communication by utilizing the IPv6, inaccordance with the Mobile IPv6 procedures.

Let's consider the case where the IPv4/v6 mobile node supporting both ofMobile IPv4 and Mobile IPv6 inside the IPv4/v6 network moves to anotherIPv4/v6 network. Because the foreign IPv4/v6 network can executecommunication by utilizing both of IPv4 and IPv6, the IPv4/v6 mobilenode can exchange the messages with both of the IPv4 mobile agent andthe IPv6 mobile agent on the network in accordance with the proceduresof the Mobile IPv4 and the Mobile IPv6. Therefore, the movement of thisIPv4/v6 mobile node between the networks is supported by both of theMobile IPv4 and the Mobile IPv6. In consequence, the IPv4/v6 mobile nodethat has moved to the foreign network can successively executecommunication without changing setting of the IP address and withoutcutting off the network connection that has been established alreadywith other IPv4 node or the IPv6 node before its movement by utilizingthe IPv4 or IPv6. It can also execute afresh communication with othernode by utilizing the IPv4 and the IPv6.

Next, let's consider the case where the IPv4/v6 mobile node moves fromthe IPv4/v6 network to the IPv4 network which can execute communicationin accordance with only the IPv4 and supports the Mobile IPv4. In thiscase, since communication by utilizing the IPv4 is possible between theIPv4/v6 mobile node and the IPv4 mobile agent, the assistance ofmovement of this mobile node between the networks by the Mobile IPv4 canbe made. Therefore, the IPv4/v6 mobile node can execute communicationsuccessively after the movement without cutting off the networkconnection that has been previously established already with other IPv4node by utilizing the IPv4. The mobile node can also executecommunication afresh by utilizing the IPv4.

However, the mobile node cannot execute communication by utilizing theIPv6 on the IPv4 network and consequently, the exchange of the messageon the IPv4 network in accordance with the Mobile IPv6 procedure becomesimpossible between the IPv4/v6 mobile node and the IPv6 mobile agent. Inother words, the assistance of the movement of the mobile node to theIPv4 network in accordance with the Mobile IPv6 becomes impossible andthe IPv4/v6 mobile node that has moved to the IPv4 network cannotmaintain the network that has been established already with other IPv6node by utilizing the IPv6 before the movement and consequently, cannotexecute communication. This mobile node cannot execute afreshcommunication with other node on the IPv4 network by utilizing the IPv6,either.

Similarly, let's consider the case where the IPv4/v6 mobile node movesfrom the IPv4/v6 network to the IPv6 network which can executecommunication by utilizing only the IPv6 and supports the Mobile IPv6.In this case, too, the IPv4/v6 mobile node cannot execute communicationby utilizing the IPv4 on the IPv6 network. In consequence, the exchangeof the message in accordance with the Mobile IPv4 procedure is notpossible on the IPv6 network between the IPv4/v6 mobile agent and theIPv4 mobile agent, so that the assistance of the movement of this mobilenode to the IPv6 network in accordance with the Mobile IPv4 becomesimpossible on the IPv6 network.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a mobilenode, a mobile agent and a network system which can successivelymaintain the network connection the IPv6 that has been establishedalready by utilizing the IPv6 before the movement when the IPv4/v6mobile node moves from the IPv4/v6 network to the IPv4 network, andwhich can also execute afresh communication by utilizing the IPv6.

It is another object of the present invention to provide a controlmethod of a mobile node, a mobile agent and a network system forassisting the movement, which can execute communication by utilizing theIPv4 between an IPv4/v6 mobile node and other IPv4 node even when theIPv4/v6 mobile node moves from an IPv4/v6 network to an IPv6 network,without changing at all existing IPv6 mobile agents and existing IPv4/v6mobile agents and without changing setting of the address of the IPv4/v6mobile node.

According to one aspect of the present invention, there is provided amobile node including IPv4 (Internet Protocol version 4) processingmeans for executing services in accordance with the IPv4, IPv6 (InternetProtocol version 6) processing means for executing services inaccordance with the IPv6, and communication processing means forexecuting transmission/reception control of packets to and fromnetworks, and moving between IP networks, wherein the mobile nodefurther comprises movement registration processing means for adding anIPv4 header (IP header used for the IPv4), in which the IPv4 address ofa mobile agent is set as a foreign address and the IPv4 address of themobile node usable in a foreign IPv4 network is set as a home address,to a message used for the IPv6 for registering the movement to a mobileagent connected to the IPv4/v6 network to assist the movement of themobile node, and transmitting the message, when this mobile node movesfrom the IPv4/v6 network (a network capable of executing communicationby utilizing both of the IPv4 and the IPv6) to an IPv4 network (anetwork capable of executing communication by utilizing only the IPv4).

In the mobile node according to the aspect of the invention describedabove, the IPv4 header is added to the message used for the IPv6 and themessage is then transmitted. Therefore, the message to be used for theIPv6 can be substantially transmitted from the foreign IPv4 network, andthe information necessary for the network connection utilizing the IPv6can be registered to the mobile agent.

According to another aspect of the present invention, there is provideda mobile agent including IPv4 processing means for executing services inaccordance with an IPv4, IPv6 processing means for executing services inaccordance with an IPv6 and communication processing means for executingtransmission/reception control of packets to and from networks, andmoving between the networks, wherein the mobile agent further comprisespacket transmission processing means for generating an IPv4 encapsulatedIPv6 packet by adding an IPv4 header, in which the IPv4 address of themobile agent is set as a foreign address and the IPv4 address of amobile node usable in a foreign IPv4 network is set as a home address,to an IPv6 packet (packet used for the IPv6) to be transmitted to othernode, and transmitting the IPv4 encapsulated IPv6 packet so generated.

In the mobile agent according to the aspect of the invention describedabove, after the IPv4 header is added to the IPv6 packet, the packet istransmitted. Therefore, the IPv6 packet can be transmitted substantiallyfrom the foreign IPv4 network.

According to still another aspect of the present invention, there isprovided a mobile node including IPv4 processing means for executingservices in accordance with the IPv4, IPv6 processing means forexecuting services in accordance with the IPv6 and communicationprocessing means for executing transmission/reception control of packetsto and from networks, and moving between the networks, wherein themobile node further comprises movement detection means for detectingwhether the mobile node has moved from the network in which a mobileagent used by this mobile node exists to another IPv4 network or to anIPv6 network (network capable of executing communication by utilizingonly the IPv6) or to an IPv4/v6 network, and movement status managementmeans for managing the movement status so detected.

Since the mobile node according to this aspect of the inventionautomatically detects the kind of the network in which the mobile nodeitself exists at present and manages itself, the necessity for adding anIPv4 header to the message used for the IPv6 or the IPv6 packet can bejudged appropriately.

According to still another aspect of the present invention, there isprovided a mobile agent for assisting the movement of a mobile nodeexecuting communication by utilizing an IPv6, including IPv4 processingmeans for executing services in accordance with an IPv4, IPv6 processingmeans for executing services in accordance with the IPv6 andcommunication processing means for executing transmission/receptioncontrol of packets to and from networks, wherein the mobile agentfurther comprises mobile node management means for managing the IPv4address of a mobile node usable in a foreign IPv4 network when receivinga message for use in the IPv6 for registering the movement, to which anIPv4 header transmitted from the mobile node to the IPv6 network to themobile agent when the mobile agent moves to the IPv4 network is added,and movement assistance processing means for adding an IPv4 header, inwhich the IPv4 address of the mobile node usable in a foreign IPv4network is set as a foreign address and the IPv4 address of the mobileagent is set as a home address, to the message used for the IPv6 topermit registration of the movement to the mobile node, and transmittingthe message.

In the mobile agent according to the aspect of the invention describedabove, after the IPv4 header is added to the message used for the IPv6and then the message is transmitted. Therefore, the message used for theIPv6 can be transmitted substantially to the mobile node that is movingto the IPv4 network.

According to still another aspect of the present invention, there isprovided a mobile agent for assisting the movement of a mobile nodeexecuting communication by utilizing the IPv6, including IPv4 processingmeans for executing services in accordance with the IPv4, IPv6processing means for executing services in accordance with the IPv6 andcommunication processing means for executing transmission/receptioncontrol of packets to and from networks, wherein the mobile agentfurther comprises transfer-to-other node processing means for deletingthe IPv4 header when receiving an IPv4 encapsulated IPv6 packettransmitted by the mobile node, and transmitting again the IP packet sotaken out to the network.

In the mobile agent according to the aspect of the invention describedabove, after only the IPv6 packet is taken out from the IPv4encapsulated IPv6 packet, the IPv6 is again transmitted. Therefore, theIPv6 packet can be transmitted substantially from the mobile node, thatis moving to the IPv4 network, to the node on the IPv6 network or on theIPv4/v6 network.

According to still another aspect of the present invention, there isprovided a mobile agent for assisting the movement of a node executingcommunication by utilizing the IPv6, including IPv4 processing means forexecuting services in accordance with the IPv4, IPv6 processing meansfor executing services in accordance with the IPv6 and communicationprocessing means for executing transmission/reception control of packetsto and from networks, wherein the mobile agent further comprisestransfer-to-other node processing means for generating an IPv4encapsulated IPv6 packet by adding an IPv4 header, in which the IPv4address of a foreign node usable in a foreign IPv4 network is set as aforeign IPv4 address and the IPv4 address of the mobile agent is set asa home IPv4 address, to the received IPv6 packet when receiving thisIPv6 packet transmitted by other node to the mobile node that has movedto the IPv4 network, and for transmitting this IPv4 encapsulated IPv6packet.

In the mobile agent according to the aspect of the invention describedabove, after the IPv4 header is added to the IPv6 packet, the IPv6packet is transmitted. Therefore, the IPv6 packet can be transmittedsubstantially from the node on the IPv6 network or on the IPv4/v6network to the mobile node that is moving to the IPv4 network.

According to still another aspect of the present invention, there isprovided a network system in which an IPv4/v6 network and an IPv4network are connected with each other by a connecting device or by theconnection device and a third network, wherein the mobile agentaccording to the fourth, fifth or sixth aspect is provided on theIPv4/v6 network and the mobile node according to the first, second orthird aspect is provided on the IPv4/v6 network or on the IPv4 network.

The network system according to the aspect described above cansuccessively keep the network connection, which utilizes the IPv6 andhas been already established before the movement of the IPv4/v6 node,when the IPv4/v6 node moves from the IPv4/v6 network to the IPv4network, and can execute afresh communication by utilizing the IPv6.

According to still another aspect of the present invention, there isprovided a method of controlling a mobile node by a mobile agent in anetwork system in which a first IP network capable of executingcommunication in accordance with first and second kinds of IPs and asecond IP network capable of executing communication in accordance withonly the first kind of IP, so that the mobile node capable of executingcommunication in accordance with the second kind of IP can communicatewith other node belonging to the first IP network in accordance with thesecond kind of IP when the mobile node moves from the first IP networkto the second IP network, which method comprises the steps of adding afirst kind of IP header, in which the IP address of a second mobileagent belonging to the second IP network in accordance with the firstkind of IP is set as a foreign address by the first mobile agentbelonging to the first IP network and the IP address of the first mobileagent in accordance with the first kind of IP is set as a home address,to an IP packet transmitted in accordance with the second kind of IPfrom other node to the mobile node, and transmitting the IP packet tothe second mobile agent; and deleting the first kind of IP header by thesecond mobile agent and transmitting the IP packet to the mobile node.

On the other hand, the IP packet may be transmitted to other node byadding the first kind of IP header, in which the IP address of the firstmobile agent in accordance with the first kind of IP is set as a foreignaddress by the second mobile agent and the IP address of the secondmobile agent in accordance with the first kind of IP is set as a homeaddress, to the IP packet in accordance with the second kind of IPtransmitted from the mobile node to other node, transmitting this IPaddress to the first mobile agent, deleting the first kind of IP headerby the first mobile agent and then transmitting the IP packet to othernode.

Alternatively, it is possible to employ a method comprising adding thefirst kind of IP header, in which the IP address of the first mobileagent in accordance with the first kind of IP is set as a foreignaddress by the second mobile agent and the IP address of the secondmobile agent in accordance with the first kind of IP is set as a homeaddress, to a movement registration request message in accordance withthe second kind of IP that is received from the mobile node,transmitting this message to the first mobile agent, adding the firstkind of IP header, in which the IP address of the second mobile agent inaccordance with the first kind of IP is set as a foreign address by thefirst mobile agent and the IP address of the first mobile agent inaccordance with the first kind of IP is set as a home address, to amessage in accordance with the second kind of IP for permitting themovement, and transmitting this message to the second mobile agent.

The present invention provides also a network system for assisting themovement of the mobile node, having the features described above.

Furthermore, the present invention provide the first and second mobileagents for assisting the movement of the mobile node, having thefeatures described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural view of a network system according to oneembodiment of the present invention;

FIG. 2 is a structural view of a movement status management table usedin an IPv4/v6 mobile node shown in FIG. 1;

FIG. 3 is a structural view of a mobile node management table used in anIPv6 mobile agent shown in FIG. 1;

FIG. 4 is a flowchart showing an IPv4/v6 movement processing in theIPv4/v6 mobile node shown in FIG. 1;

FIG. 5 is a flowchart showing a movement detection processing in theIPv4/v6 shown in FIG. 1;

FIG. 6 is a flowchart showing an IPv4 movement registration processingin the IPv4/v6 mobile node shown in FIG. 1;

FIG. 7 is a flowchart showing an IPv6 movement registration processingin the IPv4/v6 mobile node shown in FIG. 1;

FIG. 8 is a flowchart showing an IPv4-only movement registrationprocessing in the IPv4/v6 mobile node shown in FIG. 1;

FIG. 9 is a flowchart showing an IPv6 packet transmission processing inthe IPv4/v6 mobile node shown in FIG. 1;

FIG. 10 is a flowchart showing an IPv6 movement assistance processing inan IPv6 mobile agent shown in FIG. 1;

FIG. 11 is a flowchart showing a transfer-to-mobile node processing inthe IPv6 mobile agent shown in FIG. 1;

FIG. 12 is a flowchart showing a transfer-to-other node processing inthe IPv6 mobile agent shown in FIG. 1;

FIG. 13 is a structural view of an IPv6 movement registration requestmessage;

FIG. 14 is a structural view of an IPv4 encapsulated IPv6 movementregistration request message;

FIG. 15 is a structural view of an IPv4 encapsulated IPv6 packet;

FIG. 16 is a structural view of an IPv4 encapsulated IPv6 movementregistration permission message;

FIG. 17 is a structural view of an IPv6 encapsulated IPv6 packet;

FIG. 18 is a structural view showing an example of a network to whichthe present invention is applied;

FIG. 19 is an explanatory view showing a structural example of a mobilenode management table used in a home IPv6 mobile agent shown in FIG. 18;

FIG. 20 is an explanatory view showing a structural example of a mobileagent address table used in a foreign IPv6 mobile agent shown in FIG.18;

FIG. 21 is an explanatory view showing a structural example of amovement assistance management table used in the foreign IPv6 mobileagent shown in FIG. 18;

FIG. 22 is an operation flowchart showing an example of the procedure ofan IPv4 movement processing in an IPv4/v6 mobile node shown in FIG. 18;

FIG. 23 is an operation flowchart showing an example of the procedure ofan IPv6 movement processing in the IPv4/v6 mobile node shown in FIG. 18;

FIG. 24 is an operation flowchart showing an example of the procedure ofan IPv6 movement assistance processing in a home IPv6 mobile agent shownin FIG. 18;

FIG. 25 is an operation flowchart showing an example of the procedure ofa foreign IPv6 mobile agent shown in FIG. 18;

FIG. 26 is an operation flowchart showing an example of the procedure ofa transfer-to-foreign IPv6 mobile agent processing in the home IPv6mobile agent shown in FIG. 18;

FIG. 27 is an operation flowchart showing an example of the procedure ofa transfer-to-other node processing in the home IPv6 mobile agent shownin FIG. 18;

FIG. 28 is an operation flowchart showing an example of the procedure ofa transfer-to-home IPv6 mobile agent processing in the foreign IPv6mobile agent shown in FIG. 18;

FIG. 29 is an operation flowchart showing an example of the procedure ofa transfer-to-mobile node processing in the foreign IPv6 mobile agentshown in FIG. 18;

FIG. 30 is an explanatory view showing a structural example of an IPv6movement registration request message;

FIG. 31 is an explanatory view showing a structural example of a packetobtained by encapsulating an IPv6 encapsulated IPv6 packet by IPv4encapsulation;

FIG. 32 is a structural view showing another example of a network towhich the present invention is applied;

FIG. 33 is an explanatory view showing a structural example of a mobilenode management table used in a home IPv4 mobile agent shown in FIG. 32;

FIG. 34 is an explanatory view showing a structural example of a mobileagent address table used in the foreign IPv4 mobile node shown in FIG.32;

FIG. 35 is an explanatory view showing a structural example of amovement assistance management table used in the foreign IPv4 mobileagent shown in FIG. 32;

FIG. 36 is an operation flowchart showing an example of the procedure ofan IPv4 movement assistance processing in a home IPv4 mobile agent shownin FIG. 32;

FIG. 37 is an operation flowchart showing an example of the procedure ofthe foreign IPv4 movement assistance processing in the foreign IPv4mobile agent shown in FIG. 32;

FIG. 38 is an operation flowchart showing an example of the procedure ofa transfer-to-foreign IPv4 mobile agent processing in a home IPv4 mobileagent shown in FIG. 32;

FIG. 39 is an operation flowchart showing an example of the procedure ofa transfer-to-other node processing in the home IPv4 mobile agent shownin FIG. 32;

FIG. 40 is an operation flowchart showing an example of the procedure ofa transfer-to-home IPv4 mobile agent in the foreign IPv4 mobile agentshown in FIG. 32;

FIG. 41 is an operation flowchart showing an example of the procedure ofa transfer-to-mobile node processing in the foreign IPv4 mobile agentshown in FIG. 32;

FIG. 42 is an explanatory view showing a structural example of an IPv4movement registration request message;

FIG. 43 is an explanatory view showing a structural example of a packetobtained by IPv6 encapsulation of an IPv4 movement registrationpermission message;

FIG. 44 is an explanatory view showing a structural example of a packetobtained by IPv6 encapsulation of an IPv4 movement registration requestmessage; and

FIG. 45 is an explanatory view showing a structural example of a packetobtained by IPv6 encapsulation of an IPv4 packet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will beexplained with reference to the accompanying drawings.

FIG. 1 is a structural view showing a network system according to oneembodiment of the present invention.

This network system 1 includes a LAN (Local Area Network)-a 100 whichmakes use of both an IPv4 and an IPv6, a LAN-b 101 which makes use ofonly the IPv4 and a WAN (Wide Area Network) 102 which connects the LAN-a100 and the LAN-b 101 by a public line or an exclusive line.

On the LAN-a 100 exist an IPv4 node 103, an IPv6 node 104, an IPv4mobile agent-a 105 for assisting the movement of a node executingcommunication by utilizing the IPv4 by the procedure in accordance witha Mobile IPv4 between the networks, an IPv4/v6 mobile node 106 and anIPv6 mobile agent 107 for assisting the movement of the node whichexecutes communication by utilizing the IPv4 and IPv6 and also executescommunication by utilizing the IPv6 between the networks. The IPv6mobile agent 107 functions also as a router and connects the LAN-a 100and the WAN 102.

An IPv4 mobile agent-b 108 and a router 109 exist on the LAN-b 101. Therouter 109 connects the LAN-b 101 and the WAN 102.

In this embodiment, the following IP addresses are allocated,respectively: IPv4 address IPv6 address LAN-a 100 “10.0.0.0”“::11.0.0.0” IPv4 node 103 “10.0.0.10” IPv6 node 104 “::11.0.0.30”IPv4/v6 mobile node 106 “10.0.0.1” “::11.0.0.1” IPv4 mobile agent-a 105“10.0.0.11” IPv6 mobile agent 107 “10.0.0.20” “::11.0.0.20” LAN-b 101“20.0.0.0” IPv4 mobile agent-b 108 “20.0.0.11”

The IPv4/v6 mobile node 106 includes an IPv4/v6 movement processingportion 114 for executing various processings when the node moves toanother network, a movement detection processing portion 115 forexecuting a detection processing which detects the movement to anothernetwork, an IPv4 movement registration processing portion 116 forexecuting a movement notification processing which notifies the movementof the node to another IPv4 network or to an IPv4/v6 network, to theIPv4 mobile agent-a 105, an IPv6 movement registration processingportion 117 for executing a movement notification processing whichnotifies the movement of the node to another IPv6 network or to theIPv4/v6 network, to the IPv6 mobile agent 107, an IPv4-only movementregistration processing portion 118 for executing a movementnotification processing which notifies the movement of the node toanother IPv4 network to the IPv6 mobile agent 107, a movement statusmanagement table 119 for managing the movement status, an IPv4processing portion 111 for executing a processing in accordance with theservices offered by the IPv4, an IPv6 processing portion 112 forexecuting a processing in accordance with the services offered by theIPv6, an IPv6 packet transmission processing portion 113 for executing atransmission processing of the IPv6 packet, and a communicationprocessing portion 110 for executing a transmission/reception control ofthe packet to and from the LAN.

Among the constituent elements of the IPv4/v6 mobile node 106 describedabove, the present invention disposes specifically the movementdetection processing portion 114, the IPv4-only movement registrationprocessing portion 118, the IPv6 packet transmission processing portion113 and the movement status management table 119.

The IPv6 mobile agent 107 includes an IPv6 movement assistanceprocessing portion 121 which receives the movement report (a reportrepresenting the movement to the IPv6 network or to the IPv4/v6 network)from the IPv6 mobile node (not shown in the drawing) effectingcommunication by utilizing the IPv4/v6 mobile node 106 or IPv6 andmoving between the networks, and assists the mobile node, a mobile nodemanagement table 126 for managing the movement status information of themobile nodes, an IPv4 processing portion 122 for executing a processingin accordance with the services offered by the IPv4, a transferprocessing portion 123 to another node, for transferring the packetwhich is transmitted by the IPv4/v6 mobile node 106 to the IPv6 node104, an IPv6 processing portion 124 for executing a processing inaccordance with the services offered from the IPv6, a transferprocessing portion 125 to a mobile node, for transferring the packetwhich is transmitted from the IPv6 node 104 to the IPv4/v6 mobile node106, and a communication processing portion 120 for executingtransmission/reception control of the packet to the LAN.

Among the constituent elements of the IPv6 mobile agent 107 describedabove, it is the IPv6 movement assistance processing portion 121, thetransfer processing portion 123 to another node, the transfer processingportion 125 to a mobile node, and a mobile node management table 126that constitute the characterizing part of the present invention.

FIG. 2 shows a structural example of the movement status managementtable 119.

This movement status management table 119 has the following fields:

-   -   own IPv4 address 200:

This is the IPv4 address of the IPv4/v6 mobile node 106 on the LAN-a 100on which the IPv6 mobile agent 107 for assisting the movement of theIPv4/v6 mobile node 106 exists.

-   -   own IPv4 network address 201:

This is the IPv4 network address of the LAN-a 100 on which the IPv6mobile agent 107 for assisting the movement of the Ipv4/v6 mobile node106 exists.

-   -   own IPv6 address 202:

This is the IPv6 address of the IPv4/v6 mobile node 106 on the LAN-a 100on which the IPv6 mobile agent 107 for assisting the movement of theIPv4/v6 mobile node 106 exists.

-   -   own IPv6 network address 203:

This is the IPv6 network address of the LAN-a 100 on which the IPv6mobile agent 107 for assisting the movement of the IPv4/v6 mobile node106 exists.

-   -   IPv4 mobile agent IPv4 address 204:

This is the IPv4 address of the IPv4 mobile agent-a 105 on the LAN-a 100on which the IPv4 mobile agent-a 105 for assisting the movement of theIPv4/v6 mobile node 106 exists.

-   -   IPv6 mobile agent IPv4 address 205:

This is the IPv4 address of the IPv6 mobile agent 107 on the LAN-a 100on which the IPv6 mobile agent 107 for assisting the movement of theIPv4/v6 mobile node 106 exists.

-   -   IPv6 mobile agent IPv6 address 206:

This is the IPv6 address of the IPv6 mobile agent 107 on the LAN-a 100on which the IPv6 mobile agent 107 for assisting the movement of theIPv4/v6 mobile node 106 exists.

-   -   post-movement IPv4 network address 207:

This is the IPv4 network address of the network on which the IPv4/v6mobile node 106 exists at the present moment.

-   -   pre-movement IPv4 network address 208:

This is the IPv4 network address of the network before the IPv4/v6mobile node 106 moves.

-   -   post-movement IPv6 network address 209:

This is the IPv6 network address of the network in which the IPv4/v6mobile node 106 exists at the present moment. When the network existingat present is the IPv4 network, “NULL” is set.

-   -   pre-movement IPv6 network address 210:

This is the IPv6 network address of the network before the IPv4/v6mobile node 106 moves. When the network before the movement is the IPv4network, “NULL” is set.

Incidentally, the network address of the LAN-a 100 in which the IPv6mobile agent 107 for assisting the movement of the IPv4/v6 mobile node106 exists is set at the time of initialization to the field of each ofthe post-movement IPv4 network address 207, the pre-movement IPv4network address 208, the post-movement IPv6 network address 209 and thepre-movement IPv6 network address 210.

FIG. 3 shows a structural example of the mobile node management table126.

This mobile node management table 126 includes the following entries:

-   -   mobile node IPv6 address 30:

This is the IPv6 address of the mobile node the movement of which isassisted by the IPv6 mobile agent 107.

-   -   foreign IPv6 address 31:

This is the IPv6 address on the network on which the mobile node existsat the present moment. When the network existing at present is the IPv4network, “NULL” is set.

-   -   foreign IPv4 address 32:

This is the IPv4 address on the network on which the mobile node existsat the present moment. When the network existing at present is the IPv6network, “NULL” is set.

Incidentally, the entry of the mobile node does not exist in the mobilenode management table 126 at the time of initialization.

FIG. 4 is a flowchart showing the IPv4/v6 movement processing 40executed by the IPv4/v6 movement processing portion 114.

Initialization of the movement status management table 119 is effectedat Step 41.

At the next Step 50, the movement detection processing portion 115 iscaused to repeatedly execute a movement detection processing 50.

FIG. 5 is a flowchart showing the movement detection processing 50executed by the movement detection processing portion 115.

At Step 51, the IPv4/v6 mobile node 106 transmits a message transmissionrequest message for detecting the IPv4 movement and a messagetransmission request message for detecting the IPv6 movement, whichrequest an IPv4 movement detection message and an IPv6 movementdetection message for detecting the movement to another IPv4 network,the IPv6 network or the IPv4/v6 network, respectively. The IPv4 mobileagent and the IPv6 mobile agent that receive these message transmissionrequest message for detecting the IPv4 movement and message transmissionrequest message for detecting the IPv6 movement, respectively, transmitthe IPv4 movement detection message and the IPv6 movement detectionmessage, respectively. In addition, the IPv4 mobile agent and the IPv6mobile agent periodically transmit the IPv4 movement detection messageand the IPv6 movement detection message, respectively.

Next, a timer is set at Step 52.

If the IPv4 movement detection message is received at Step 53, the flowproceeds to Step 54 and when it is not, the flow proceeds to Step 55.

At Step 54, the network address of the network, to which the IPv mobileagent transmitting the received IPv4 movement detection message belongsis compared with the post-movement IPv4 network address 207 inside themovement status management table 119. If they are the same networkaddress, the flow proceeds to Step 55 and if they are different networkaddresses, the flow proceeds to Step 60.

If the IPv6 movement detection message is received at Step 55, the flowproceeds to Step 56 and if it is not, the flow proceeds to Step 57.

At Step 56, the network address of the network to which the IPv6 mobileagent transmitting the IPv6 movement detection message received belongsis compared with the post-movement IPv6 network address 209 inside themovement status management table 119. If they are the same networkaddress, the flow proceeds to Step 57 and if they are different networkaddresses, the flow proceeds to Step 70.

At Step 57, the flow returns to Step 53 if the time is not out, andproceeds to Step 58 if the time is out.

At Step 58, whether or not the post-movement IPv4 network address 207inside the movement status management table 119 and the pre-movementIPv4 network address 208 are different addresses and whether or not thepost-movement IPv6 network address 209 and the pre-movement IPv6 networkaddress are the same network address are judged, and if the result ofthis judgement proves Yes, the flow proceeds to Step 80 and if theresult proves No, the processing is completed.

At Step 60, the IPv4 movement registration processing portion 116 iscaused to execute the IPv4 movement registration processing 60.

At Step 70, the IPv6 movement registration processing portion 117 iscaused to execute the IPv6 movement registration processing 70.

At Step 80, the IPv4-only movement registration processing portion 118is caused to execute the IPv4-only movement registration processing 80.

The movement detection processing 50 described above will be explainedmore concretely. When the IPv4/v6 mobile node 106 exists on the LAN-a100 at the present moment, it receives the IPv4 movement detectionmessage and the IPv6 movement detection message transmitted by the IPv4mobile agent-a 105 and by the IPv6 mobile agent 107, respectively. Inthis instance, since the network address (=“10.0.0.0”) of the LAN-a 100to which the IPv4 mobile agent-a 105 transmitting the IPv4 movementdetection message belongs is the same as the post-movement IPv4 networkaddress 207 (=10.0.0.0”) of the movement status table 119, it ispossible to know that the mobile node does not move to another IPv4network or another IPv4/v6 network. Therefore, the flow proceeds fromStep 54 to Step 55 but Step 60 (IPv4 movement registration processing)is not executed. Since the network address (=“::11.0.0.0”) of thenetwork to which the IPv6 mobile agent 107 transmitting the IPv6movement detection message belongs is the same as the post-movement IPv6network address 209 (=“::11.0.0.0”) of the movement status table 119, itis possible to know that the mobile node does not move to another IPv6or another IPv4/v6 network. Therefore, the flow proceeds from Step 56 toStep 57 but Step 70 (IPv6 movement registration processing) is notexecuted.

Next, when the IPv4/v6 mobile node 106 has moved to the LAN-b 101 at thepresent moment, this mobile node 106 receives the IPv4 movementdetection message transmitted by the IPv4 mobile agent-b 108. Since thenetwork address (=“20.0.0.0”) of the LAN-b 101 to which the IPv4 mobileagent-b 108 transmitting the IPv4 movement detection message belongs isdifferent from the post-movement IPv4 network address 207 (=“10.0.0.0”)of the movement status table 119, it is possible to know that theIPv4/v6 mobile node 106 has moved to another IPv4 network or anotherIPv4/v6 network. Therefore, the flow proceeds from Step 54 to Step 60,where the IPv4 movement registration processing 60 is executed. As willbe described later with reference to FIG. 6, the premovement IPv4network address 208 of the movement status table 119 is updated to“10.0.0.0” and the post-movement IPv4 network address 207 is updated to“20.0.0.0”, by this IPv4 movement registration processing 60.

On the other hand, because the IPv6 mobile agent does not exist in theLAN-b 101, the IPv6 movement detection message is not received. Inconsequence, the flow proceeds from Step 55 to Step 57 and theprocessing of Steps 56 and 70 (IPv6 movement registration processing) isnot executed.

Because the post-movement IPv4 network address 207 (=“20.0.0.0”) of themovement status table 119 is different from the pre-movement IPv4network address 208 (=“10.0.0.0”) and because the post-movement IPv6network address 209 (=“::11.0.0.0”) is the same as the pre-movement IPv6network address 210 (=“::11.0.0.0”) after time-out, it is possible toknow that the mobile node has moved to the IPv4 network. Therefore, theflow proceeds from Step 58 to Step 80 and the IPv4-only movementregistration processing 80 is executed.

Incidentally, when the IPv4/v6 mobile node 106 moves to another IPv4/v6network such as the LAN-a 100, both of the IPv4 movement detectionmessage and the IPv6 movement detection message are received. Therefore,both of the IPv4 movement registration processing 60 and the IPv6movement registration processing 70 are executed. On the other hand, thepost-movement IPv4 network address 207 of the movement status table 119becomes inequal (≠) to the pre-movement IPv4 network address 208 and thepost-movement IPv6 network address 209 becomes inequal (≠) to thepre-movement IPv6 network address 210. Therefore, the flow does notproceed from Step 58 to Step 80 and the IPv4-only movement registrationprocessing 80 is not executed.

FIG. 6 is a flowchart showing an example of the IPv4 movementregistration processing executed by the IPv4 movement registrationprocessing portion 116. Incidentally, this IPv4 movement registrationprocessing 60 is the processing which follows the processing procedureof the Mobile IPv4.

At Step 61, the IPv4 network address 201 of the movement statusmanagement table 119 of its own is compared with the network address ofthe network to which the IPv4 mobile agent transmitting the IPv4movement detection message belongs. When they are not the same networkaddress, it is possible to know that the mobile node has moved toanother network, and the flow proceeds to Step 62. When they are thesame network address, on the other hand, it is possible to know that themobile node has returned to the LAN-a 100 in which the IPv6 mobile agent107 assisting the movement of the IPv4/v6 mobile node 106 exists, andthe flow then proceeds to Step 63.

At Step 62, the IPv4 address on the foreign network which the IPv4/v6mobile node 106 can make use of is acquired. This IPv4 address can beacquired by utilizing a DHCP for executing automatic distribution of theaddresses or by manual setting, for example.

At Step 63, the IPv4 movement registration request message istransmitted to the IPv4 mobile agent registered to the IPv4 mobile nodeIPv4 address 204 of the movement status management table 119.

At Step 64, the movement registration permission message as the reply tothe IPv4 movement registration request message is awaited from the IPv4mobile agent, and after this IPv4 movement registration permissionmessage is received, the flow proceeds to Step 65.

At Step 65, the post-movement IPv4 network address 207 of the movementstatus management table 119 is substituted for the pre-movement IPv4network address 208 and then the network address of the network to whichthe IPv4 mobile agent transmitting the IPv4 movement detection messageis substituted for the post-movement IPv4 network address 207.

The IPv4 movement registration processing 60 described above will beexplained more concretely. When the IPv4/v6 mobile node 106 moves fromthe LAN-a 100 to the LAN-b 101, the flow proceeds from Step 61 to Step62 and further to Step 63, and transmits the IPv4 movement registrationrequest message to the IPv4 mobile agent-a 105. After the IPv4 movementregistration permission is received from the IPv4 mobile agent-a 105,the flow proceeds from Step 64 to Step 65. Next, “10.0.0.0” is set tothe pre-movement IPv4 network address 208 while “20.0.0.0”, is set tothe post-movement IPv4 network address 207.

FIG. 7 is a flowchart showing an example of the IPv6 movementregistration processing executed by the IPv6 movement registrationprocessing portion 117. Incidentally, this IPv6 movement registrationprocessing 70 is the processing that follows the processing procedure ofthe Mobile IPv6.

At Step 71, own IPv6 network address 203 of the movement statusmanagement table 119 is compared with the network address of the networkto which the IPv6 mobile agent transmitting the IPv6 movement detectionmessage belongs. When they are not the same network address, it ispossible to know that the mobile node has moved to another network andthe flow proceeds to Step 72. When they are the same network address, onthe other hand, it is possible to know that the mobile node has returnedto the LAN-a 100 in which the IPv6 mobile agent 107 assisting themovement of the IPv4/v6 mobile node 106 exists, and the flow thenproceeds to Step 73.

At Step 72, the IPv6 address on the foreign network which the IPv4/v6mobile node 106 can make use of is acquired. Acquisition of this IPv6address is made by utilizing the DHCP for executing automaticdistribution of the addresses or by manual setting, for example.

At Step 73, the IPv6 movement registration request message istransmitted to the IPv6 mobile agent registered to the IPv6 mobile agentIPv6 address 206 of the movement status management table 119. This IPv6movement registration request message contains its own IPv6 address1301, the foreign IPv6 address 1302 and the foreign IPv4 address 303 asshown in FIG. 13. This IPv6 movement registration processing 70 sets theIPv6 address held by own IPv6 address 202 of the movement statusmanagement table 119 to its own IPv6 address 1301, the foreign IPv6address to the foreign IPv6 address 1302 and “NULL” to the foreign IPv4address 1303.

At Step 74, the IPv6 movement registration permission message as thereply to the IPv6 movement registration request message is awaited fromthe IPv6 mobile agent, and after this permission message is received,the flow proceeds to Step 75.

At Step 75, the post-movement IPv6 network address 209 of the movementstatus management table 119 is substituted for the pre-movement IPv6network address 210 and then the network address of the network to whichthe IPv6 mobile agent transmitting the IPv6 movement detection messagebelongs is substituted for the post-movement IPv6 network address 209.

FIG. 8 is a flowchart showing an example of the IPv4-only movementregistration processing executed by the IPv4-only movement registrationprocessing portion 118.

At Step 81, the IPv4 encapsulated IPv6 movement registration requestmessage is transmitted to the IPv6 mobile agent registered to the IPv6mobile agent IPv6 address 206 of the movement status management table119. As shown in FIG. 14, this IPv4 encapsulated IPv6 movementregistration request message contains an IPv4 header 1401 and an IPv6movement registration request message 1300. The IPv4 header 1401contains in turn a foreign IPv4 address 1402 and a source IPv4 address1403. The address of the IPv6 mobile agent IPv4 address 205 of themovement status management table 119 is set to the foreign IPv4 address1402 and the IPv4 address acquired in the foreign IPv4 network is set tothe source IPv4 address 1403. The IPv6 movement registration requestmessage 1300 shown in FIG. 14 contains its own IPv6 address 1301, theforeign IPv6 address 1302 and the foreign IPv4 address 1303 as shown inFIG. 13.

The IPv4-only movement registration processing 80 sets the IPv6 addressheld by the IPv6 address 202 of the movement status management table 119to its own IPv6 address 1301, “NULL” to the foreign IPv6 address 1302and the IPv4 address at the destination to the foreign IPv4 address1303.

At Step 82, the IPv4 encapsulated IPv6 movement registration permissionrequest message as the reply to the IPv4 encapsulated IPv6 movementregistration request message is awaited from the IPv6 mobile agent, andafter this IPv4 encapsulated IPv6 movement registration permissionmessage is received, and the flow proceeds to Step 83. Incidentally, theIPv4 processing portion 111 removes the IPv4 header from the IPv4encapsulated IPv6 movement registration permission message (thisprocedure will be hereinafter called the “IPv4 decapsulation”) anddelivers it to the IPv4-only movement registration processing portion118. This IPv4 decapsulation in the IPv4 processing portion 111 is oneof the services offered by the existing IPv4.

At Step 83, the post-movement IPv6 network address 209 of the movementstatus management table 119 is substituted for the pre-movement IPv6network address 210 and then “NULL” is substituted for the post-movementIPv6 network address 209.

The IPv4-only movement registration processing 80 described above willbe explained more concretely. When the IPv4/v6 mobile node 106 has movedfrom the LAN-a 100 to the LAN-b 101, the following IPv4 encapsulatedIPv6 movement registration request message 1400 is generated at Step 81.

-   -   IPv4 header:        -   foreign IPv4 address 1402: “10.0.0.20” (IPv4 address of IPv6            mobile agent 107)        -   home IPv4 address 1403: “20.0.0.1” (IPv4 address that the            IPv4/v6 mobile node 106 uses afresh on the LAN-b 101)    -   IPv6 movement registration message 1300:        -   own IPv6 address 1301: “::11.0.0.1”        -   foreign IPv6 address 1302: “NULL”        -   foreign IPv6 address 1303: “20.0.0.1”

The IPv4 encapsulated IPv6 movement registration permission message 1400is transmitted to the IPv6 mobile agent 107.

Next, after the IPv4 encapsulated IPv6 movement registration permissionmessage is received from the IPv6 mobile agent 107 at Step 82,“::11.0.0.1” is set to the pre-movement IPv6 network address 210 at Step83 and “NULL” is set to the post-movement IPv6 network address 209.

FIG. 9 is a flowchart showing an example of the IPv6 packet transmissionprocessing 90 executed by the IPv6 packet transmission processingportion 113 of the IPv6 processing portion 112 in the IPv4/v6 mobilenode 106.

At Step 91, the IPv6 packet transmission request by the networkapplication, etc., is awaited, and the flow proceeds to Step 92 if thetransmission request is made.

At Step 92, whether or not the IPv6 network address 209 after themovement of the movement status management table 119 is “NULL” ischecked and if it is “NULL”, the flow proceeds to Step 93 and if it isnot, the flow proceeds to Step 94.

At Step 93, since the destination is the IPv4 network, the IPv6 packetis encapsulated by IPv4 encapsulation and is transmitted. In otherwords, the IPv4 header 1401 is added to the IPv6 packet 1501 as shown inFIG. 15, the IPv6 mobile agent IPv4 address 205 of the movement statusmanagement table 119 is set to the foreign IPv4 address 1402 of thatIPv4 header 1401, the IPv4 address acquired by the foreign IPv4 networkis set to the home IPv4 address, and the IPv4 encapsulated IPv6 packet1500 is generated and transmitted. The flow then returns to Step 91described above.

At Step 94, since the destination is the IPv6 network or the IPv4/v6network, the IPv6 is transmitted as such. The flow then returns to Step91 described above.

The IPv6 packet transmission processing 90 will be explained moreconcretely. When the IPv4/v6 mobile node 106 moves from the LAN-a 100 tothe LAN-b 101, for example, the IPv4/v6 mobile node 106 receives thetransmission request of the IPv6 packet 1501 by the network applicationat Step 91. Then, “10.0.0.20” (IPv4 address of the IPv6 mobile agent107) is set as the foreign IPv4 address to this IPv6 packet 1501 at Step92 and furthermore, the IPv4 header 1401 to which “20.0.0.1” is set asthe home IPv4 address 1403 is added. The IPv6 packet encapsulated bythis IPv4 encapsulation is transmitted to the IPv6 mobile agent 107.

FIG. 10 is a flowchart showing an example of the IPv6 movementassistance processing 1000 executed by the IPv6 movement assistanceprocessing portion 121 of the IPv6 mobile agent 107.

At Step 1001, whether or not the message transmission request messagefor detecting the IPv6 movement is received from the IPv6 mobile node(not shown in the drawing) or the IPv4/v6 mobile node 106 is checked,and if it is, the flow proceeds to Step 1002 and if it is not, the flowproceeds to Step 1003.

At Step 1002, the IPv6 movement detection message is transmitted to thenode which transmits the IPv6 movement detection message transmissionrequest message described above.

At Step 1003, whether or not the IPv6 movement registration requestmessage 1300 is received is checked, and if it is, the flow proceeds toStep 1004 and if it is not, the flow returns to Step 1001.

At Step 1004, whether or not the movement registration request can beaccepted is checked, and if it cannot be accepted, the flow proceeds toStep 1005 and if it can, the flow proceeds to Step 1006.

At Step 1005, the IPv6 movement registration rejection message istransmitted to the node that transmits the IPv6 movement registrationrequest message 1300. The flow then returns to Step 1001 describedabove.

At Step 1006, own IPv6 address 1301 of the IPv6 movement registrationrequest message 1300 is compared with the foreign IPv6 address 1302 andwhen they are the same address, the flow proceeds to Step 1007 and whenthey are different addresses, the flow proceeds to Step 1008.

At Step 1007, the information of the corresponding mobile node insidethe mobile node management table 126 is deleted by judging that thismobile node returns to its own network. The flow then proceeds to Step1011.

At Step 1008, the foreign IPv4 address 1303 inside the IPv6 movementregistration request message 1300 is checked, and if “NULL” is set, theflow proceeds to Step 1009 and if it is not, the flow proceeds to Step1010.

At Step 1009, the information of the mobile node is set to the mobilenode management table 126 by judging that this mobile node moves to theIPv6 network or to the IPv4/v6 network. In other words, the value of theforeign IPv6 address 1302 inside the IPv6 movement registration requestmessage 1300 so received is set to the foreign IPv6 address 31 insidethe mobile node management table 126 and “NULL” is set to the foreignIPv4 address 32. The flow then proceeds to Step 1011.

At Step 1010, the information of the corresponding mobile node is set tothe mobile node management table 126 by judging that this mobile nodehas moved to the IPv4 network. In other words, “NULL” is set to theforeign IPv6 address 31 inside the mobile node management table 126while the value of the foreign IPv4 address 1303 inside the IPv6movement registration request message 1300 so received is set to theforeign IPv4 address 32. The flow then proceeds to Step 1012.

At Step 1011, the IPv6 movement registration permission message istransmitted to the mobile node, and the flow returns to Step 1001described above.

At Step 1012, the IPv6 movement registration permission messageencapsulated by IPv4 encapsulation is transmitted to the mobile node. Inother words, as shown in FIG. 16, the IPv4 header 1401 is added to theIPv6 movement registration permission message 1601, and the foreign IPv4address 1303 inside the IPv6 movement registration request message 1300is set to the foreign IPv4 address 1402 of the IPv4 header 1401.Further, the IPv4 address of the IPv6 mobile agent 107 is set to thehome IPv4 address 1403 and the IPv4 encapsulated IPv6 movementregistration permission message is generated and transmitted. The flowthen returns to Step 1001.

Incidentally, when the IPv4/v6 mobile node 106 moves to the IPv4network, the IPv4/v6 mobile node 106 transmits the IPv4 encapsulatedIPv6 movement registration request message 1300 to the IPv6 mobile agent107 as described already. When the IPv6 mobile agent 107 receives thisIPv4 encapsulated IPv6 movement registration request message 1300, IPv4decapsulation of this message is executed at the IPv4 processing portion122 and the IPv6 movement registration request message 1300 is taken outand delivered to the IPv6 movement assistance processing portion 121.Since this processing is one of the services offered by the existingIPv4, any new function need not be added to the IPv4 processing portion122.

The IPv6 movement assistance processing 1000 described above will beexplained more concretely. When the IPv4/v6 mobile node 106 has movedfrom the LAN-a 100 to the LAN-b 101, the flow proceeds serially to Steps1001, 1002, 1003 and 1004, and since the foreign IPv6 address 1302(=“NULL”) inside the IPv6 movement registration request message 1300 isdifferent from own IPv6 address 1301 (=“::11.0.0.1”) at Step 1005, theflow proceeds to Step 1008.

At Step 1008, since the foreign IPv4 address 1303 (=“20.0.0.1”) insidethe IPv6 movement registration request message 1300 is not “NULL”, theflow proceeds to Step 1010. At this Step 1010, “::11.0.0.1” isregistered to the mobile node IPv6 address 30 in the mobile nodemanagement table 126 as the information of the IPv4/v6 mobile node 106,“20.0.0.1” is registered to the foreign IPv4 address 32, and “NULL” isregistered to the foreign IPv6 address 31. At Step 1012, the IPv4 header1401 to which “20.0.0.1” is set as the foreign IPv4 address 1402 and“10.0.0.20” is set as the home IPv4 address 1403 is added to the IPv6movement registration permission message 1601 and is transmitted to theIPv4/v6 mobile node 106.

FIG. 11 is a flowchart showing an example of the transfer-to-mobile nodeprocessing 1100 which is executed by the transfer-to-mobile nodeprocessing portion 125 of the IPv6 processing portion 124 in the IPv6mobile agent 107.

At Step 1101, reception of the IPv6 packet to the mobile node registeredto the mobile node management table 126 among the IPv6 packetstransmitted by the IPv6 node 104 and other IPv6 nodes (not shown in thedrawing) is awaited, and after this packet is received, the flowproceeds to Step 1102.

At Step 1102, whether or not the foreign IPv6 address 31 of thecorresponding mobile node inside the mobile node management table 126 is“NULL” is checked, and if it is “NULL”, the flow proceeds to Step 1103and if it is not, the flow proceeds to Step 1104.

At Step 1103, the mobile node as the destination of the IPv6 packet isjudged as moving to the IPv4 network, and the IPv6 packet isencapsulated by IPv4 encapsulation and is transmitted to the IPv4network to which the mobile node as the destination of this packet ismoving. The structure of the IPv4 encapsulated IPv6 packet at this timeis shown in FIG. 15. The foreign IPv4 address 32 of the correspondingmobile node inside the mobile node management table 126 is set to theforeign IPv4 address 1402 and the IPv4 address of the IPv6 mobile agent107 is set to the home IPv4 address 1403. The flow then returns to Step1101.

At Step 1104, the mobile node as the destination of the IPv6 packet isjudged as moving to the IPv6 network or to the IPv4/v6 network, and theIPv6 header is added afresh to the IPv6 packet (this processing will behereinafter called “IPv6 encapsulation”) and is transmitted to the IPv6network or to the IPv4/v6 network to which the mobile node is moving. Inother words, as shown in FIG. 17, the IPv6 header 1701 is added to theIPv6 packet 1704, the foreign IPv6 address 31 of the correspondingmobile node inside the mobile node management table 126 is set to theforeign IPv6 address 1702 of its IPv6 header 1701, the IPv6 address ofthe IPv6 mobile agent 107 is set to the home IPv6 address 1703 and theIPv6 encapsulated IPv6 packet 1700 is generated and transmitted. Theflow then returns to Step 1101. Incidentally, the processing procedurefor encapsulating the IPv6 packet by the IPv6 encapsulation is theprocedure that follows the Mobile IPv6.

The transfer-to-mobile node processing 1100 described above will beexplained more concretely. When the IPv4/v6 mobile node 106 has movedfrom the LAN-a 100 to the LAN-b 101, “::11.0.0.1” is set as theinformation of the IPv4/v6 mobile node 106 to the mobile node IPv6address 30 inside the mobile node management table 126 by the IPv6movement assistance processing 1000 described already, “NULL” is set tothe foreign IPv6 address 31 and “20.0.0.1” is set to the foreign IPv4address 32. Therefore, when the IPv6 mobile agent 107 receives the IPv6packet addressed to the IPv4/v6 mobile node 106, it adds the header IPv4header 1401, in which “20.0.0.1” is set to the foreign IPv4 address 1402and “10.0.0.20∞ is set to the home IPv4 address 1403, to this IPv6packet and transfers it to the IPv4/v6 mobile node 106 of the LAN-b 101.This IPv4 encapsulated IPv6 packet 1500 is received by the IPv4/v6mobile node 106, is IPv4-decapsulated by the IPv4 processing portion 111and is processed as the ordinary IPv6 packet.

In this way, even when the IPv4/v6 mobile node moves from the LAN-a 100as the IPv4/v6 network to the LAN-b 101 as the IPv4 network, this mobilenode can receive the IPv6 packet transmitted by the IPv6 node 104 of theLAN-a 100.

FIG. 12 is a flowchart showing an example of the transfer-to-other nodeprocessing 1200 executed by the transfer-to-other node processingportion 123 of the IPv4 processing portion 122 in the IPv6 mobile agent107.

At Step 1201, the mobile agent awaits the reception of the IPv4 packetaddressed to its own (IPv6 mobile agent 107) and when this packet isreceived, the flow proceeds to Step 1202.

At Step 1202, whether or not the IPv4 packet so received is the IPv6packet encapsulated by IPv4 encapsulation is checked, and when it is theIPv4 encapsulated IPv6 packet, the flow proceeds to Step 1203 and whenit is not, the flow proceeds to Step 1205.

At Step 1203, whether or not the home node of the IPv4 encapsulated IPv6packet is the mobile node registered to the mobile node management table126 is checked, and if it is registered, the flow proceeds to Step 1204and if it is not, the flow proceeds to Step 1205.

At Step 1204, the IPv4 encapsulated IPv6 packet is decapsulated by IPv4decapsulation and is transmitted to the network where the node as thedestination exists. The flow then returns to Step 1201.

At Step 1205, the IPv4 packet so received is discarded. The flow thenreturns to Step 1201.

The transfer-to-other node processing 1200 described above will beexplained more concretely. Let's consider the case where the IPv4/v6mobile node 106 transmits the IPv6 packet to the IPv6 node 104. In thisinstance, the IPv6 packet is subjected to IPv4 encapsulation by the IPv6packet transmission processing 90 by using the IPv4 header 1401 in which“10.0.0.20” is set as the foreign IPv4 address 1402 (addressed to theIPv6 mobile agent 107) and “20.0.0.1” is set as the home IPv4 address1403, and the IPv4 encapsulated IPv6 packet is transmitted to the IPv6mobile agent 107. Receiving this packet, the IPv6 mobile agent 107removes the IPv4 header 1401 of the IPv4 encapsulated IPv6 packet atStep 1204 after passing through Steps 1201, 1202 and 1203, and transmitsthe IPv6 packet 1501 to the LAN-a 100 in which the IPv6 node 104 as theaddress exists. This IPv6 packet is received as the ordinary IPv6 packetby the IPv6 node 104.

As described above, even when the mobile node has moved from the LAN-a100 as the IPv4/v6 network to the LAN-b 101 as the IPv4 network, theIPv4/v6 mobile node 106 can transmit the IPv6 packet to the IPv6 node104 of the LAN-a 100.

Incidentally, communication utilizing the IPv4 between the IPv4/v6mobile node 106 and other nodes can be carried out by the movementassistance of the nodes in the IPv6 by the IPv4 mobile agent-1 105 andthe IPv4 mobile agent-b 108 supporting the Mobile IPv4 as the existingmethod.

When the IPv4/v6 mobile node 106 returns from the LAN-b 101 to the LAN-a100, the IPv4/v6 mobile node 106 detects the movement to the IPv6 or tothe IPv4/v6 network by the movement detection processing describedabove. The mobile node is judged as returning to the LAN-a 100 by theIPv6 movement registration processing 70, and transmits the IPv6movement registration request message 1300 in which “::11.0.0.1” is setto its own IPv6 address, “::11.0.0.1” which is the same as its own IPv6address 1301 to the foreign IPv6 address 1302 and “NULL” to the foreignIPv4 address 1303, to the IPv6 mobile agent 107.

Receiving the IPv6 movement registration request message 1300, the IPv6mobile agent 107 judges that the IPv4/v6 mobile node 106 returns to theLAN-a 100 because its own IPv6 address inside the IPv6 movementregistration request message 1300 is the same as the foreign IPv6address 1302, and omits the information on the IPv4/v6 mobile node 106inside the mobile node management table 126. As a result, the IPv4/v6mobile node 106 can make communication utilizing the ordinary IPv6.

Incidentally, the IPv4/v6 mobile node 106 reports its return to theLAN-a 100 to the IPv4 mobile agent-a 105, too, by the IPv4 movementregistration request message in accordance with the Mobile IPv4processing procedure and for this reason, communication utilizing theordinary IPv4 can be made, too.

The embodiment given above automatically detects the movement betweenthe networks by utilizing the IPv4 movement detection message and theIPv6 movement detection message, but it is also possible to employ theconstruction in which the user of the mobile node reports by himself tothe movement detection processing portion 116 so as to execute the IPv4movement registration processing 60, the IPv6 movement registrationprocessing 70 or the IPv4-only movement registration processing 80.

Next, another embodiment of the present invention will be explained withreference to the drawings.

First, the explanation will be given on the case where the IPv4/v6mobile node moves from the IPv4/v6 network to the IPv4 network.

A structural example of the network system to which the presentinvention is applied and a structural example of the mobile agent willbe explained with reference to FIG. 18. As shown in the drawing, thenetwork system according to this embodiment includes a LAN-a 1800, aLAN-b 1801 and a WAN 1802 that connects the LAN-a 1800 and the LAN-b1801 by a public line or an exclusive line. On the LAN-a 1800 exist anIPv4 node 1803 which executes communication by utilizing only the IPv4as a protocol of a network layer as the third layer of an OSI referencemodel, an IPv6 node 1804 which executes communication by utilizing onlythe IPv6, an IPv4 mobile agent-a 1805 which assists the movement betweenthe networks for the nodes executing communication by utilizing the IPv4in accordance with the procedure of the Mobile IPv4, an IPv4/v6 mobilenode 1806 which executes communication by utilizing both IPv4 and IPv6and moves between the networks, and a home IPv6 mobile agent 1807 whichassists the movement of a node when the node executing communication byutilizing the IPv6 modes to another network.

On the LAN-b 1801 exist an IPv4 mobile agent-b 1808 and a foreign IPv6mobile agent 1809 which assists the movement of a node when the nodeexecuting communication by utilizing the IPv4 and the IPv6 and executingcommunication by utilizing IPv6 comes to the LAN-b 1801.

Incidentally, the home IPv6 mobile agent 1807 functions also as a routerhandling both of the IPv4 packet and the IPv6 packet and connects theLAN-a 1800 and the WAN 1802. The router 1810 handling only the IPv4packet connects the LAN-b 1801 and the WAN 1802. Therefore, whereas bothof the IPv4 packet and the IPv6 packet can come out from the networksbeyond the router from the LAN-a 1800, only the IPv4 packet can come outfrom the LAN-b 1801. Incidentally, transmission/reception itself of theIPv4 packet and the IPv6 packet can be made inside the LAN-a 1800 andthe LAN-b 1801.

In this embodiment, the IP addresses are listed below: IPv4 address IPv6address IPv4 node 1803 “10.0.0.10” IPv6 node 1804 “11::20” IPv4/v6mobile node 1806 “10.0.0.30” “11::30” IPv4 mobile agent-a 1805“10.0.0.11” home IPv6 mobile agent 1807 “10.0.0.1” “11::1” IPv4 mobileagent-b 1808 “20.0.0.11” foreign IPv6 mobile agent 1809 “20.0.0.1”“21::1”

The IPv4/v6 mobile node 1806 comprises an IPv4 movement processingportion 1813 which executes a processing in accordance with the MobileIPv4 when the node moves to another IPv4 network or to an IPv4/v6network, an IPv6 movement processing portion 1815 which executes aprocessing in accordance with the Mobile IPv6 when the mobile node movesto another IPv6 network or to an IPv4/v6 network, an IPv4 processingportion 1812 which executes a processing in accordance with the servicesoffered by the IPv4, an IPv6 processing portion 1814 which executes aprocessing in accordance with the services offered by the IPv6 and acommunication processing portion 1811 which executes atransmission/reception control, etc. of a packet to the LAN.

The home IPv6 mobile agent 1807 comprises an IPv6 movement assistanceportion 1817 which assists the movement for the mobile node (notparticularly shown in the drawing) executing communication by utilizingthe IPv6 and moving between the networks or for an IPv6 mobile node1806, a mobile node management table 1822 which manages the informationof the mobile node that has moved to another IPv6 network or to theIPv4/v6 network, an IPv6 processing portion 1818 which executes aprocessing in accordance with the services offered by the IPv4, atransfer-to-other node processing portion 1819 which executes a transferprocessing of the IPv6 packet, which is transferred from the foreignIPv6 mobile agent 1809 and is transmitted by the IPv4/v6 mobile node1806, to the IPv6 node as the destination, an IPv6 processing portion1820 which executes a processing in accordance with the services offeredby the IPv6, a transfer-to-foreign IPv6 mobile agent processing portion1821 which executes a transfer processing of the IPv6 packet, which istransmitted from another IPv6 node to the IPv4/v6 mobile node 1806, tothe foreign IPv6 mobile agent 1809 and a communication processingportion 1816 which executes a transmission/reception control, etc. ofthe packet to the LAN.

The foreign IPv6 mobile agent 1809 comprises a foreign IPv6 movementassistance portion 1823 which assists the movement of the IPv4/v6 mobilenode 1806 when this node 1806 moves to the network (LAN-b 1801) to whichthe foreign IPv6 mobile agent 1809 belongs, a movement assistancemanagement table 1828 which manages the information of this mobile node1806, a mobile agent address table 1830 which registers the addressinformation of the home IPv6 mobile agent 1807, an IPv4 processingportion 1824 which executes a processing in accordance with the servicesoffered by the IPv4, a transfer-to-mobile node processing portion 1825which executes a processing for transferring the packet, which istransferred from the home IPv6 mobile agent 1807 and is addressed to theIPv4/v6 mobile node 1806, to the IPv4/v6 mobile node 1806, an IPv6processing portion 1826 which executes a processing in accordance withthe services offered by the IPv6, a transfer-to-home IPv6 mobile agentprocessing portion 1812 which executes a processing for transferring theIPv6 packet, which is transmitted by the IPv4/v6 mobile node 1810 toanother IPv6 node, to the home IPv6 mobile agent 1807, and acommunication processing portion 1829 which executes atransmission/reception control, etc. of the packet to the LAN.

Among the constituent elements of the home IPv6 mobile agent 1807described above, it is the IPv6 movement assistance portion 1817, thetransfer-to-other node processing portion 1819, the transfer-to-foreignIPv6 mobile agent processing portion 1821 and the mobile node managementtable 1822 that constitute the characterizing part of the presentinvention. Among the constituent elements of the foreign IPv6 mobileagent 1809, it is the foreign IPv6 movement assistance portion 1823, thetransfer-to-mobile node processing portion 1825, the transfer-to-homeIPv6 mobile agent processing portion 1827, the mobile agent addresstable 1830 and the mobile agent management table 1828 that constitutethe characterizing part of the present invention.

FIG. 19 shows an example of the mobile node management table 1822. Asshown in this drawing, the mobile node management table 1822 includes amobile node IPv6 address 1920 as the IPv6 address of the mobile node,the foreign IPv6 address 1921 representing the IPv6 address which themobile node makes use of in the foreign IPv6 network or in the foreignIPv4/v6 network, and a foreign IPv6 mobile agent IPv4 address 1922representing the IPv4 address of the foreign IPv6 mobile agent 109.Here, when the mobile node moves to the IPv6 network or to the IPv4/v6network, “NULL” is set to the foreign IPv6 mobile agent IPv4 address1922 and when the mobile node moves to the IPv4 network, the IPv4address of the foreign IPv6 mobile agent 1809 existing inside thatnetwork is set to the address 1922. Incidentally, though the drawingshows the case where the entries for a plurality of mobile nodes exist,the entry of the mobile node does not exist in this table under theinitial state. Further, the updating processing of this table will bedescribed later.

FIG. 20 shows an example of the mobile agent address table 1830described above. As shown in this drawing, the mobile agent addresstable 1830 includes the home IPv6 mobile agent IPv4 address 2030 and thehome IPv6 mobile agent IPv6 address 2031 as the IPv4 address and theIPv6 address of all the home IPv6 mobile agents existing in the networksystem (though this embodiment represents only the home IPv6 mobileagent 1807 on LAN-a 1800). This table is set by a manager, for example.

FIG. 21 shows an example of the movement assistance management table1828 described above. As shown in the drawing, the movement assistancemanagement table 1828 includes a mobile node IPv6 address 2140 as theIPv6 address of the IPv4/v6 mobile node 1806, a home IPv6 mobile agentIPv4 address 2141 as the IPv4 address of the home IPv6 mobile agent 1807existing in the home network of the mobile node, and a registration flag2142 representing whether the entry is “tentative registration” or “realregistration”. Incidentally, though this drawing represents the casewhere the entries for a plurality of mobile nodes exist, the entry ofthe mobile node does not exist in this table under the initial state.The updating processing of this table will be described later.

In the construction described above, the processings of the IPv4/v6mobile node 1806, the home IPv6 mobile agent 1807 and the foreign IPv6mobile agent 1809 when the IPv4/v6 mobile node 1806 moves from the LAN-a1800 as the IPv4/v6 network to the LAN-b 1801 as the IPv4 network, andhandling of each table described above, will be explained next indetail.

FIG. 22 is a flowchart showing an example of the processing of the IPv4movement processing portion 1812 for detecting whether or not theIPv4/v6 mobile node 1806 has moved to another IPv4 network or to theIPv4/v6 network, and for executing various processings when the mobilenode has moved. By the way, this IPv4 movement processing portion 1812executes the processing in accordance with the processing procedure ofthe Mobile IPv4.

The IPv4 movement processing portion 1812 first transmits the messagetransmission request message for detecting the IPv4 movement as themessage for requesting the transmission of the IPv4 movement detectionmessage, which is in turn the message for detecting the movement of themobile node to another IPv4 network or to the IPv4/v6 network (Step2251). Incidentally, the IPv4 movement detection message is transmittedby the IPv4 mobile agent either periodically or when it receives thetransmission request message of the IPv4 movement detection. Next, theIPv4 movement processing portion 1812 judges whether or not the IPv4movement detection message is received (Step 2252). When the IPv4movement detection message is received (Step 2252YES), the IPv4 movementprocessing portion 1812 judges from this message whether or not themobile node moves to another network (Step 2253). Incidentally, thenetwork address information is set inside the IPv4 movement detectionmessage, and the movement is detected by comparing this addressinformation with the IPv4 address of the IPv4/v6 mobile node 1806 of itsown.

When the movement of the mobile node to another network is found as aresult of the judgement described above (Step 2253YES), the IPv4movement processing portion 1812 judges next whether or not the networkas the visiting network is the home network of the IPv4/v6 mobile node1806 (the LAN-a 1800 is the home network in this embodiment) (Step2254). The IPv4 movement detection message is utilized at the time ofthis judgement, too. When it is not the home network as a result of thisjudgement, (Step 2254NO), the IPv4 movement processing portion 1812 thenacquires the foreign IPv4 address that is used by the IPv4 mobile node-a1805 when it transfers the IPv4 packet bound to the IPv4/v6 mobile node1806 to the mobile node that is moving to another network (Step 2255).The IPv4/v6 mobile node 1806 acquires this foreign IPv4 address from theaddresses offered by the IPv4 mobile agent-b 1808 or by utilizing theDHCP that automatically distributes the addresses, or by manual setting.

To report and register the movement to the IPv4 mobile agent-a 1805, theIPv4 movement processing portion 1812 transmits the IPv4 movementregistration message (Step 2256). Thereafter, the IPv4 movementprocessing portion 1812 waits for the IPv4 movement registrationpermission message as the reply of the IPv4 movement registrationrequest message from the IPv4 mobile agent-a 1805 (Step 2257) and afterthis message is received (Step 2257YES), the flow returns again to thefirst step 2251. The IPv4 movement processing portion 1812 repeats theprocessing described above.

FIG. 23 is a flowchart showing an example of the processing of the IPv6movement processing portion 1815 for detecting whether or not theIPv4/v6 mobile terminal 1806 has moved to another IPv6 network or to theIPv4/v6 network and for executing various processings when this mobilenode has moved. Incidentally, this IPv6 movement processing portion 1815executes the processing in accordance with the procedure of the MobileIPv6.

The IPv6 movement processing portion 1815 first transmits the messagetransmission request message for detecting the IPv6 movement, which isthe message for requesting the transmission of the IPv6 movementdetection message as the message for detecting the movement to anotherIPv6 network or to the IPv4/v6 network (Step 2361). Incidentally, thisIPv6 movement detection message is transmitted by the IPv6 mobile agenteither periodically or when it receives the message transmission requestmessage for detecting the IPv6 movement. Next, the IPv6 movementprocessing portion 1815 judges whether or not the IPv6 movementdetection message is received (Step 2362). When this IPv6 movementdetection message is received (Step 2362YES), the IPv6 movementprocessing portion 1815 judges from this message whether or not themobile node has moved to another network (Step 2362). Incidentally, thenetwork address information is set into the IPv6 movement detectionmessage, and the movement detection is executed by comparing thisaddress information with its own IPv6 address of the IPv4/v6 mobileterminal 1806.

If the result of judgement represents that the mobile node has moved toanother network (Step 2363YES), the IPv6 movement processing portion1815 judges next whether or not the visiting network is the home network(the LAN-a 1800 is the home network in this embodiment) (Step 2364). TheIPv6 movement detection message is utilized for this judgement, too.When the destination of the movement is not the home network as a resultof the judgement described above (Step 2364NO), the IPv6 movementprocessing portion 1815 then acquires the IPv6 address that can be usedin the visiting network. Acquisition of this IPv6 address is made byutilizing the DHCP which automatically distributes the address, by theaddress automatic generation function as one of the functions offered bythe IPv6, or by manual setting. In order to report and register themovement to the home IPv6 mobile agent 1807, the IPv6 movementprocessing portion 1815 transmits the IPv6 movement registration requestmessage (Step 2366).

FIG. 30 shows the data structure of the IPv6 movement registrationrequest message transmitted by the IPv4/v6 mobile node 1806. As shown inthe drawing, the IPv6 movement registration request message 3000includes a IPv6 header 3001 and a IPv6 data 3004. The IPv6 header 3001includes a foreign IPv6 address 3002 and a home IPv6 address. The IPv6address of the home IPv6 mobile agent 1807 is set to the home IPv6address 3002, and the IPv6 address which the IPv4/v6 mobile node 1806acquires in the visiting network is set to the home IPv6 address 3003.The IPv6 data 3004 includes the IPv6 address 3005 as the IPv6 address ofthe node itself transmitting this message and the foreign IPv6 address3006 as the IPv6 address which the mobile node acquires afresh in thevisiting network. When the IPv4/v6 mobile node 1806 returns to the LAN-a1800 as the home network, the same address as its own IPv6 address 3005is set to the foreign IPv6 address 3006.

Thereafter, the IPv6 movement processing portion 1815 awaits until theIPv6 movement registration permission message as the reply of the IPv6movement registration request message 3000 is received from the homeIPv6 mobile agent 1807 (Step 2367) and after this message is received(Step 2367YES), the flow returns again to the initial Step 2361.Thereafter, the IPv6 movement processing portion 1815 repeats theprocessing described above.

FIG. 24 is a flowchart showing an example of the processing of the IPv6movement assistance processing portion 1817 which executes theassistance processing for the movement of the IPv6 mobile node (notparticularly shown in the drawing) or the IPv4/v6 mobile node 1806between the networks.

The IPv6 movement assistance processing portion 1817 first judgeswhether or not the IPv6 movement detection message transmission messageis received (Step 2401). When this message is found received as a resultof this judgement (Step 2401YES), the IPv6 movement assistanceprocessing portion 1817 transmits the IPv6 movement detection message(Step 2402). The IPv6 movement assistance processing portion 1817 thenjudges whether or not the IPv6 movement registration request message3000 is received (Step 2403). If the message is found received as aresult of judgement (Step 2403YES), the IPv6 movement assistanceprocessing portion further judges whether or not the request for thismovement registration is acceptable (Step 2404). If the request is foundunacceptable as a result of judgement (Step 2404NO), the IPv6 movementassistance processing portion 1817 transmits the IPv6 movementregistration rejection message as the registration rejection replymessage of the IPv6 movement registration request message 3000 to themobile node.

If the request is acceptable (Step 2404YES), the IPv6 movementassistance processing portion 1817 then compares its own IPv6 address3005 inside the message with the foreign IPv6 address (Step 2406). Ifthey are found the same as a result of this comparison (Step 2406YES),the IPv6 movement assistance processing portion 1817 judges that themobile node has returned to the home network, and deletes thecorresponding information of the mobile node inside the mobile nodemanagement table 1812 (Step 2407). Then, the IPv6 movement assistanceprocessing portion 1817 transmits the IPv6 movement registrationpermission message as the registration permission reply message of theIPv6 movement registration request message 3000 to the mobile node (Step2411).

When the Ipv6 address 3005 and the foreign IPv6 address 3006 are foundas the different addresses as a result of comparison (Step 2406NO), theIPv6 movement assistance processing portion 1817 further judges whetheror not the IPv6 movement registration request message 300 so received isencapsulated by IPv4 encapsulation and transferred from the foreign IPv6mobile agent 1809 (Step 2008). Incidentally, IPv4 encapsulation of theIPv6 movement registration request message 3000 by the foreign IPv6mobile agent 1809 is effected by the later-appearing foreign IPv6movement assistance processing portion 1823 inside the foreign IPv6mobile agent 1809. When the home IPv6 mobile agent 1807 receives thisIPv4 encapsulated IPv6 movement registration request message 3000, itsown IPv4 processing portion 1818 executes IPv4 decapsulation anddelivers the decapsulated message to the IPv6 movement assistanceprocessing portion 1817. This IPv4 decapsulation by the IPv4 processingportion 1818 is one of the services offered by the existing IPv4.

When the message is not judged as being-transferred as a result of thejudgement as to IPv4 decapsulation and transfer (Step 2408NO), the IPv6movement assistance processing portion 1817 judges that the mobile nodehas moved to another IPv6 network or to the IPv4/v6 network and sets theinformation of this mobile node to the mobile node management table1822. At this time, the value of the foreign IPv6 address 3006 insidethe IPv6 movement registration request message 3000, which is received,is set to the foreign IPv6 address 1921 inside the mobile nodemanagement table 1822 and “NULL” is set to the foreign IPv6 mobile agentIPv4 address 1922 (Step 2409). The IPv6 movement assistance processingportion 1817 then transmits the IPv6 movement registration permissionmessage to the mobile node (Step 2411).

When the message is found as being IPv4 encapsulated and transferred asa result of the judgement described above (Step 2408YES), the IPv6movement assistance processing portion 1817 judges that the mobile nodehas moved to the IPv4 network and sets the information of this mobilenode to the mobile node management table 1822. At this time, the valueof the foreign IPv6 address 3005 inside the IPv6 movement registrationrequest message 3000, which is transferred, is set to the foreign IPv6address 1921 inside the mobile node management table 1822, and the valueof the home IPv4 address inside the IPv4 header, which is added to theIPv6 movement registration request message 3000 transferred, is set tothe foreign IPv6 mobile agent IPv6 address 1922. The IPv6 movementassistance processing portion 1817 then executes IPv4 encapsulation ofthe IPv6 movement registration permission message as the reply to themobile node and transfers the message (Step 2412).

The structure of the IPv6 movement registration permission message whichis IPv4 encapsulated at this time is the same as the structure 1600shown in FIG. 16. The foreign IPv6 mobile agent IPv4 address 1922registered to the mobile node management table 1822 is set to theforeign IPv4 address 1402 inside the IPv4 header 1401, and own IPv4address of the home IPv6 mobile agent 1807 is set to the home IPv4address 1403.

The IPv6 movement assistance processing portion 1817 completes theprocessings as described above and repeats thereafter the processingdescribed above.

FIG. 25 is a flowchart showing an example of the processing of theforeign IPv6 movement assistance processing portion 1823 which executesthe movement assistance processing for the IPv4/v6 mobile node 1806between the networks at the foreign IPv6 mobile agent 1809.

The foreign IPv6 movement assistance processing portion 1823 firstjudges whether or not the message transmission request message fordetecting the IPv6 movement is received (Step 2501). When this messageis found received as a result of the judgement (Step 2501YES), theforeign IPv6 movement assistance processing portion 1823 transmits theIPv6 movement detection message (Step 2502). Next, the foreign IPv6movement assistance processing portion 1823 judges whether or not theIPv6 movement registration request message 3000 is received (Step 2503).If this message is found received as a result of the judgement (Step2503YES), the IPv6 movement assistance processing portion 1823 registerstentatively the information of this mobile node to the movementassistance management table 1828 (Step 1804). At this time, the value ofown IPv6 address 3005 inside the IPv6 movement registration requestmessage 3000 received is set to the mobile node IPv6 address 2140 of themovement assistance management table 1828, and the value of the homeIPv6 mobile agent IPv4 address 2030 corresponding to the foreign IPv6address 3002 inside the IPv6 movement registration request message 3000is set to the home IPv6 mobile agent IPv4 address 2141 by looking up themobile agent address table 1830. Further, “tentative registration” isset to the registration flag. The foreign IPv6 movement assistanceprocessing portion 1823 executes IPv4 encapsulation of the IPv6registration request message 3000 so received and transfers theencapsulated message to the home IPv6 mobile agent 1807 (Step 2505).

The structure of the IPv4 encapsulated IPv6 movement registrationrequest message at this time is the same as the structure 1400 shown inFIG. 14. The IPv4 address 2141 of the home IPv6 mobile agent 1807registered to the movement assistance management table 1828 is set tothe foreign IPv4 address 1402 in the IPv4 header 1401, and own IPv4address of the foreign IPv6 mobile agent 1809 is set to the home IPv4address 1403.

Incidentally, after movement, the IPv4/v6 mobile node 1806 alwaystransmits once the packet to the foreign IPv6 mobile agent 1809 inaccordance with the processing procedure of the Mobile IPv6. Therefore,the foreign IPv6 mobile agent 1809 can receive the IPv6 movementregistration request message 3000 address to the home IPv6 mobile agent1807.

The foreign IPv6 movement assistance processing portion 1823 sets thetimer (Step 806) and waits for the IPv6 movement registration permissionmessage 1601 as the reply of the IPv6 movement registration requestmessage 3000 for a predetermined time (Steps 2507 and 2510).Incidentally, the IPv6 movement registration permission message 1601 isencapsulated by IPv4 encapsulation and is transferred by the home IPv6mobile agent 1807 as described above.

When the IPv6 movement registration permission message 1601 is receivedwithin the predetermined time (Step 2507YES), the foreign IPv6 movementassistance processing portion 1823 updates the registration flag 2142corresponding to the mobile node, which is previously registeredtentatively to the movement assistance management table 1828, to “realregistration” assistance management table 1828, to “real registration”(Step 2508). Further, the home foreign IPv6 movement assistanceprocessing portion 1823 executes IPv4 decapsulation of the IPv6 movementregistration permission message 1601 received and transfers this messageto the IPv4/v6 mobile node 1806 (Step 2509). When the IPv6 movementregistration permission message 1601 is not received within thepredetermined time (Step 2510YES), the foreign IPv6 movement assistanceprocessing portion 1823 deletes the information of this mobile node fromthe movement assistance management table 1828 (Step 2511). The foreignIPv6 movement assistance processing portion 1823 completes theprocessings as described above and thereafter executes them repeatedly.

FIG. 26 is a flowchart showing an example of the processing of thetransfer-to-foreign IPv6 mobile agent processing portion 1821 whichtransfers the IPv6 packet, which other IPv6 node transmits to the IPv6mobile node or to the IPv4/v6 mobile node 1806, to the foreign IPv6mobile agent 1809 existing in the network to which the mobile nodemoves, at the home IPv6 mobile agent 1807.

The transfer-to-foreign IPv6 mobile agent processing portion 1821 firstjudges whether or not the IPv6 packet, which is registered to the mobilenode management table 1822 and is addressed to the mobile node, amongthe IPv6 packets transmitted by the IPv6 node 1804 or other IPv6 nodes(not shown particularly in the drawing) is received (Step 2601). If thispacket is found received as a result of the judgement, thetransfer-to-IPv6 mobile agent processing portion 1821 executes afreshIPv6 encapsulation of this packet (Step 2602).

The structure of the IPv6 packet encapsulated by IPv6 encapsulation atthis time is the same as the structure 1700 shown in FIG. 17. Thecorresponding foreign IPv6 address 1921 inside the movement assistancemanagement table 1822 is set to the foreign IPv6 address 1702 inside theIPv6 header 1701 and the IPv6 address of the home IPv6 mobile agent 1807of its own is set to the home IPv6 address 1703.

The transfer-to-foreign IPv6 mobile agent processing portion 1821 judgesnext whether or not the foreign IPv6 mobile agent IPv4 address 1922 ofthe corresponding mobile node inside the mobile node management table1822 is “NULL” (Step 2603). If the foreign IPv6 mobile agent IPv4address 1922 is found “NULL” as a result of the judgement (Step 2603NO),the transfer-to-foreign IPv6 mobile agent processing portion 1821 judgesthat the mobile node is moving to the IPv6 network or to the IPv4/v6network and transmits as such the IPv6 encapsulated IPv6 packet 1700(Step 2605). Incidentally, the processing procedures for executing IPv6encapsulation of the IPv6 packet and transmitting the packet follow theprocedures of the ordinary Mobile IPv6.

If the foreign IPv6 mobile agent IPv4 address 1922 is judged as beingother than “NULL” as a result of the judgement (Step 2603YES), thetransfer-to-foreign IPv6 mobile agent processing portion 1821 judgesthat this mobile node is moving to the IPv4 network, executes furtherIPv4 encapsulation of the IPv6 packet which has been IPv6 encapsulatedalready, and transmits it to the foreign IPv6 mobile agent 1809 (Step2604).

FIG. 31 shows the structure of the packet 3100 which is IPv4encapsulated at this time. As shown in the drawing, this packet has thestructure in which the IPv4 header 1401 is added afresh to the IPv6encapsulated IPv6 packet 1700 shown in FIG. 17. The value of thecorresponding foreign IPv6 mobile agent IPv4 address 1922 inside themobile node management table 1822 is set to the foreign IPv4 address1402 inside the IPv4 header 1401 and the value of the IPv4 address ofthe home IPv6 mobile agent 1807 of its own is set to the home IPv4address 1403.

The transfer-to-foreign IPv6 mobile agent processing portion 1821completes the processing and thereafter executes repeatedly theprocessing described above.

FIG. 27 is a flowchart showing an example of the processing executed bythe transfer-to-other node processing portion 1819 when the IPv6 packet,which the IPv4/v6 mobile node 1806 transfers to other IPv6 node on theforeign IPv4 network, is IPv4 encapsulated and transferred from theforeign IPv6 mobile agent 1809, to the foreign IPv6 node, in the homeIPv6 mobile agent 1807.

The transfer-to-other node processing portion 1819 first judges whetheror not the IPv4 packet addressed to the home IPv6 mobile agent 1807itself is received (Step 2701). If it is found received as a result ofjudgement (Step 2701YES), the transfer-to-other node processing portion1819 then judges whether or not the packet so received is encapsulatedby IPv4 encapsulation and transferred by the foreign IPv6 mobile agent1809 (Step 2702). Incidentally, the transfer of the IPv6 packet by theforeign IPv6 mobile agent 1809 is executed by the transfer-to-home IPv6mobile agent processing portion 1827 inside the foreign IPv6 mobileagent 1809 as will be described later. If it is not found thetransferred IPv6 packet as a result of judgement (Step 2702NO), thetransfer-to-other node processing portion 1819 discards this packet(Step 2705). If it is the transferred IPv6 packet (Step 2702YES), thetransfer-to-other node processing portion 1819 further judges whether ornot the home node of this IPv6 packet is the mobile node registered tothe mobile node management table 1822 (Step 2703). If it is not foundregistered as a result of this judgement (Step 2703NO), thetransfer-to-other node processing portion 1819 discards this packet(Step 2705). If it is found registered (Step 2703YES), thetransfer-to-other node processing portion 1819 decapsulates this packetby IPv4 decapsulation and transmits it to the foreign IPv6 node (Step2704).

The transfer-to-other node processing portion completes the processingand thereafter executes repeatedly the processing described above.

FIG. 28 is a flowchart showing an example of the processing executed bythe transfer-to-home IPv6 mobile agent processing portion 1827 fortransferring the IPv6 packet, which is transmitted by the IPv4/v6 mobilenode 1806 to other IPv6 node in the foreign IPv6 mobile agent 1809, tothe home IPv6 mobile agent 107.

The transfer-to-home IPv6 mobile agent processing portion 1827 firstjudges whether or not the IPv6 packet transmitted from the IPv4/v6mobile node 106 registered to the movement assistance management table1828 is received (Step 2801). If the corresponding packet is foundreceived as a result of this judgement, the transfer-to-home IPv6 mobileagent processing portion 1827 then judges whether or not theregistration flag 2142 of the corresponding mobile node inside themobile node management table 1828 is “real registration” (Step 2802). Ifit is found the “real registration” as a result of this judgement (Step2802YES), the transfer-to-home IPv6 mobile agent processing portion 1827then encapsulates the IPv6 packet so received by IPv4 encapsulation andtransmits it to the home IPv6 mobile agent 1807 (Step 2803).

The structure of the IPv6 packet which is IPv4 encapsulated at this timeis the same as the structure 1500 shown in FIG. 15.

The value of the corresponding home IPv6 mobile agent IPv4 address 2141inside the movement assistance management table 1828 is set to theforeign IPv4 address 1402 inside the IPv4 header 1401, while own IPv4address of the foreign IPv6 mobile agent 1809 itself is set to theforeign IPv4 address 1403.

If the registration flag 2142 is not found the “real registration” as aresult of the judgement (Step 2802NO), the transfer-to-home IPv6 mobileagent processing portion 1827 discards the packet (Step 2804). Thetransfer-to-home IPv6 mobile agent processing portion 1827 completes theprocessing and thereafter executes repeatedly the processing describedabove.

FIG. 29 is a flowchart showing an example of the processing of thetransfer-to-mobile node processing portion 1825 which executes theprocessing for transferring the packet to IPv4/v6 mobile node 1806 whenthe IPv6 packet, which is transmitted by other IPv6 mobile node to theIPv4/v6 mobile node 1806 by the home IPv6 mobile agent 1807 in theforeign IPv6 mobile agent 1809, is encapsulated by IPv6 encapsulation,is further encapsulated by IPv4 encapsulation and is transferred.

The transfer-to-mobile node processing portion 1825 first judges whetheror not the IPv4 packet addressed to the foreign IPv6 mobile agent 1809is received (Step 2901). If the packet is found received as a result ofthis judgement (Step 2901YES), the transfer-to-mobile node processingportion 1825 then judges whether or not the packet so received is theone encapsulated by IPv4 encapsulation and transferred by the home IPv6mobile agent 1807 (Step 2902). Incidentally, the transfer of the IPv6packet by this home IPv6 mobile agent 1807 is executed by the foreignIPv6 mobile agent processing portion 1821 described above. If the packetis not found as the transferred IPv6 packet as a result of the judgement(Step 2902NO), the transfer-to-mobile node processing portion 1825discards this packet (Step 2905). If it is found as the transferredpacket (Step 2902YES), the transfer-to-mobile node processing portion1825 further judges whether or not the foreign node of this IPv6 packetis the mobile node really registered to the movement assistancemanagement table 1828 (Step 2903). The IPv6 address of the foreign nodeis the address of the foreign node contained in the IPv6 packet 1704. Ifit not found really registered as a result of the judgement (Step2903NO), the transfer-to-mobile node processing portion 1825 discardsthis packet (Step 2905). If it is really registered (Step 2903YES), thetransfer-to-mobile node processing portion 1825 decapsulates this packetby IPv4 decapsulation and then transfers it to the IPv4/v6 mobile node1806 (Step 2904).

The transfer-to-mobile node processing portion 1825 completes theprocessing and thereafter executes repeatedly the processing describedabove.

The flow of the processings from FIGS. 22 to 29 described above will beexplained hereby with reference to the network system shown in FIG. 18.When the IPv4/v6 mobile node 1806 exists on the LAN-a 1800 as the homenetwork, the IPv4/v6 mobile node 1806 receives the IPv4 movementdetection messages and the IPv6 movement detection message transmittedby the IPv4 mobile agent-a 1805 and the home IPv6 mobile agent 1807,respectively. Therefore, it is not judged as moving.

When the IPv4/v6 mobile node 1806 has moved to the LAN-b 1801, theIPv4/v6 mobile agent 1806 receives the messages from the IPv4 mobileagent-b 1808 and the foreign IPv6 mobile agent 1809, respectively.Therefore, the mobile is judged as having moved to other network. TheIPv4/v6 mobile node 1806 transmits the IPv4 movement registrationrequest message and the IPv6 movement registration request message 3000to the IPv4 mobile agent-a 1805 and to the home IPv6 mobile agent 1807,respectively, by the IPv4 movement processing portion 1813 and the IPv6movement processing portion 1815.

To this IPv6 movement registration request message 3000 are set “11::1”(home Ipv6 mobile agent 1807) as the foreign IPv6 address 3002, “21::30”(assumed as the IPv6 address used afresh on LAN-b 1801 by the IPv4/v6mobile node 1806 in this embodiment) as the home IPv6 address 3003,“11::30” (IPv4/v6 mobile node 1806) as its own IPv6 address 3005, and“21::30” as the foreign IPv6 address 3006.

In this embodiment, the IPv6 packet cannot come out from the LAN-b 1801beyond the router as described above, but can transmit and receive theIPv6 packet inside the LAN-b 1801. Therefore, the IPv4/v6 mobile node1806 can receive the IPv6 movement detection message transmitted by theforeign IPv6 mobile agent 1809, and can also transmit the IPv6 movementregistration request message 3000 to the LAN-b 1801.

The IPv6 movement registration request message 3000 is once received bythe foreign IPv6 mobile agent 1809. The foreign IPv6 mobile agent 1809adds the IPv4 header 1401, in which “10.0.0.1” (home IPv6 mobile agent1807) is set as the foreign IPv4 address 1402 and “20.0.0.1” (foreignIPv6 mobile agent 1809) is set as the home IPv4 address 1403, to themessage by its foreign IPv6 movement assistance processing portion 1823,and transfers the message to the home IPv6 mobile agent 1807.Thereafter, this message is received by the home IPv6 mobile agent 1807.After receiving this message, the home IPv6 mobile agent 1807 adds theIPv4 header 1401, in which “20.0.0.1” (foreign IPv6 mobile agent 1809)is set as the foreign IPv4 address 1402 and “10.0.0.1” (home IPv6 mobileagent 1807) is set as the foreign IPv4 address 1403, to the IPv6movement registration permission message 1601 by its IPv6 movementassistance processing portion 1817, and transmits this message to thehome IPv6 mobile agent 1809. Receiving this message, the foreign IPv6mobile agent 1809 decapsulates this message by IPv4 decapsulation by theforeign IPv6 movement assistance processing portion 1823 and transmitsdecapsulated message to the IPv4/v6 mobile node 1806.

In consequence, registration of the movement of the IPv4/v6 mobile node1806 to the home IPv6 mobile agent 1807 is completed. At this time areset “11::30” to the mobile node IPv6 address 20, “21::30” to the foreignIPv6 address 1921, and “20.0.0.1” to the foreign IPv6 mobile agent IPv6address 2140 of the mobile node management table 1822, as theinformation of the IPv4/v6 mobile node 1806. Similarly, “11::30” is setto the mobile node IPv6 address 2140 and “10.0.0.1”, to the home IPv6mobile agent IPv4 address 2141 of the movement assistance managementtable 1828.

When the home IPv6 mobile agent 1807 receives the IPv6 packettransmitted by the IPv6 node 1804 to the IPv4/v6 mobile node 1806, itadds the IPv6 header 1701, in which “21::30” is set to the foreign IPv6address 1702 and “11::1” is set to the home IPv6 address 1703, to thisIPv6 packet by its transfer-to-foreign mobile agent processing portion1821, and further adds the IPv4 header 1401, in which “20.0.0.1” is setto the foreign IPv4 address 1402 and “10.0.0.1” is set to the home IPv4address 1403, and transfers the packet to the foreign IPv6 mobile agent1809. The packet 3100 is received by the home IPv6 mobile agent 1809.This mobile agent 1809 decapsulates this packet by IPv4 decapsulation byits transfer-to-mobile node processing portion 1825 and transmits it tothe IPv4/v6 mobile node 1806. The IPv4/v6 mobile node 1806 receives andprocesses this packet as the IPv6 packet in accordance with the ordinaryMobile IPv6 procedure.

When the home IPv6 mobile agent 1809 receives the IPv6 packettransmitted by the IPv4/v6 mobile node 1806 to the IPv6 node 1804, onthe contrary, it adds the IPv4 header 1401, in which “10.0.0.1” (homeIPv6 mobile agent 1807) is set to the home IPv4 address 1402 and“20.0.0.1” (foreign IPv6 mobile agent 1809) is set to the home IPv4address 1403, to this packet by the transfer-to-home IPv6 mobile agentprocessing portion 1827 and transmits the packet to the home IPv6 mobileagent 1807. This IPv4 encapsulated packet 1500 is received by the homeIPv6 mobile agent 1807. The home IPv6 mobile agent 1807 decapsulatesthis packet by IPv4 decapsulation by its transfer-to-other nodeprocessing portion 1819 and transmits the packet to the foreign IPv6node 1804. The foreign IPv6 node 1804 receives and processes this packetas the ordinary IPv6 packet.

In the present invention, even when the IPv4/v6 mobile node 1806 movesfrom the LAN-a 1800 as the IPv4/v6 network to the LAN-b 1801 as the IPv4network, the IPv4/v6 mobile node 1806 can receive the IPv6 packettransmitted from the IPv4/v6 mobile node 1804 to the IPv4/v6 mobile node1806 as described above. On the contrary, the existing IPv6 node 1804can receive the IPv6 packet transmitted by the IPv4/v6 mobile node 1806to the IPv6 node 1804.

Further, communication making use of the IPv4 between other nodes andthe IPv4/v6 mobile node 1806 can be made by means of the movementassistance by the IPv4 mobile agent-a 1805 supporting the Mobile IPv4 asthe existing method and the movement assistance on the IPv4 by the IPv4mobile agent-b 1808.

Incidentally, when the IPv4/v6 mobile node 1806 returns from the LAN-b1801 to the LAN-a 1800, the IPv4/v6 mobile node 1806 detects this returnto the home network by the IPv6 movement processing portion 1815described above. Then, the IPv4/v6 mobile node 1806 transmits the IPv6movement registration request message 3000 in which “11::30” is set toits own IPv6 address 3005 and “11::30” which is the same as its own IPv6address 3005 is set to the home IPv6 address 3006, to the home IPv6mobile agent 1807. Receiving this IPv6 movement registration requestmessage 3000, the home IPv6 mobile agent 1807 judges that the IPv4/v6mobile node has returned to the LAN-a 1800 as the home network becauseits own IPv6 address 3005 inside this message is the same as the foreignIPv6 address 3006, and then deletes the information about this mobilenode inside the mobile node management table 1822. In consequence, theIPv4/v6 mobile node 1806 can execute communication utilizing theordinary IPv6. Similarly, since the IPv4/v6 mobile node 1806 reports itsreturn to the LAN-a 1800 to the IPv4 mobile agent-a 1805 in accordancewith the processing procedure of the Mobile IPv4 by the IPv4 movementregistration request message. Communication utilizing the ordinary IPv4can be made, too.

In the embodiment described above, the movement of the mobile nodebetween the networks is detected by utilizing the IPv4 movementdetection message and the IPv4 detection message, but it is alsopossible to employ the system construction in which the user of themobile node indicates by himself to the IPv4 movement processing portion1813 and to the IPv6 movement processing portion and reports themovement to the IPv4 mobile agent and to the IPv6 mobile agent.

Next, the explanation will be given on the case where the IPv4/v6 mobilenode moves from the IPv4/v6 network to the IPv6 network.

A structural example of the network system to which the presentinvention is applied and a structural example of the mobile agent willbe described with reference to FIG. 32.

As shown in this drawing, the network system according to thisembodiment includes a LAN-c 3200, a LAN-d 3201 and a WAN 1902 connectingthe LAN-c 3200 and the LAN-d 3201 by a public line or an exclusive line.On the LAN-c 3200 exist an IPv4 node 3203 executing communication byutilizing only the IPv4, an IPv6 node 3204 executing communication byutilizing only the IPv6, an IPv4/v6 mobile node 1806 executingcommunication by utilizing both IPv4 and IPv6 and moving between thenetworks, a home IPv4 mobile agent-c 3206 executing communication byutilizing both IPv4 and IPv6 and assisting the movement of the node,which executes communication by utilizing the IPv4, between thenetworks, and an IPv6 mobile agent-c 3207 assisting the movement of thenode, which executes communication by utilizing the IPv6 in accordancewith the Mobile IPv6 procedure, between the networks. On the LAN-d 3201exist a foreign IPv4 mobile agent 3208 which executes communication byutilizing the IPv4 and IPv6 and assists the movement of the nodeexecuting communication by utilizing the IPv4 when this node moves tothe LAN-d 3201, and an IPv6 mobile agent-d 3209. Here, the IPv4/v6mobile node 1806 is the same as the one shown in FIG. 18.

Incidentally, the IPv6 mobile agent-c 3207 functions also as a routerhandling both of the IPv4 packet and the IPv6 packet and connects theLAN-c 3200 and the WAN 3202. The IPv6 mobile agent-d 3209 functions alsoas a router handling only the IPv6 packet and connects the LAN-d 3201and the WAN 3202. Therefore, both of the IPv4 packet and the IPv6 packetcan go out to the external networks beyond the routers, whereas only theIPv6 packet can go out from the LAN-d 3201. Incidentally,transmission/reception itself of the IPv4 packet and the IPv6 packetinside the LAN-c 3200 and the LAN-d 3201 is possible.

In this embodiment, the IP addresses are tabulated below. IPv4 addressIPv6 address IPv4 node 3203 “10.0.0.10” IPv6 node 3204 “11::20” IPv4/v6mobile node 1806 “10.0.0.30” “11::30” home IPv4 mobile agent 3206“10.0.0.1” “11::1” home IPv4 mobile agent 3208 “20.0.0.1” “21::1”

The home mobile agent 3206 includes an IPv4 movement assistance portion3216 which executes communication by utilizing the IPv4 and assists themovement of an IPv4 mobile node (not particularly shown in the drawing)moving between the networks or an IPv4/v6 mobile node 1806, a mobilenode management table 3217 which manages the information of the mobilenode that has moved to another IPv4 network or to the IPv4/v6 network,an IPv4 processing portion 3218 which executes processing in accordancewith the services offered by the IPv4, a transfer-to-foreign IPv4 mobileagent processing portion 3219 which executes a processing fortransferring the IPv4 packet, which is transmitted by other IPv4 node tothe IPv4/v6 mobile node 1806, to a foreign IPv4 mobile agent 3208, anIPv6 processing portion 3220 which executes processing in accordancewith the services offered by the IPv6, a transfer-to-other nodeprocessing portion 3221 which executes a processing for transferring theIPv4 packet, which is transferred from the foreign IPv4 mobile agent3208 and is transferred to the IPv4/v6 mobile node 1806, to the foreignIPv4 node, and a communication processing portion 3215 which executestransmission/reception control, etc. of the packet to and from the LAN.

The foreign IPv4 mobile agent 3206 comprises a foreign IPv4 movementassistance processing portion 3223 which assists the movement of theIPv4/v6 mobile node 1806 when this node 1806 moves to the network (LAN-d3201) to which the foreign IPv4 mobile agent 3208 belongs, a movementassistance management table 3229 which manages the information of themobile node, a mobile agent address table 3228 which registers theaddress information of the home IPv4 mobile agent 3206, an IPv4processing portion 3224 which executes a processing in accordance withthe services offered by the IPv4, a transfer-to-mobile agent processingportion 3225 which executes a processing for transferring the IPv4packet, which is transmitted from the IPv4/v6 mobile node 1806 to otherIPv4 node, to the home IPv4 mobile agent 3206, an IPv6 processingportion 3226 which executes a processing in accordance with the servicesoffered by the IPv6, a transfer-to-mobile node processing portion 3227which executes a processing for transferring the packet, which istransferred from the home IPv4 mobile agent 3206 to the IPv4/v6 mobilenode 1806, to the IPv4/v6 mobile node 1806, and a communicationprocessing portion 3222 which executes transmission/reception control,etc. of the packet to the LAN.

Here, among the constituent elements of the home IPv4 mobile agent 3206described above, it is the IPv4 movement assistance processing portion3216, the mobile node management table 3217, the transfer-to-foreignIPv4 mobile agent processing portion 3219 and the transfer-to-other nodeprocessing portion 3221 that constitute a characterizing part of thepresent invention. Among the constituent elements of the foreign IPv4mobile agent 3208, the constituent elements according to the presentinvention are the foreign IPv4 movement assistance portion 3223, themobile agent address table 3228, the movement assistance managementtable 3229, the transfer-to-home IPv4 mobile agent processing portion3225 and the transfer-to-mobile node processing portion 3227.

FIG. 33 shows an example of the mobile node management table 3217described above. As shown in the drawing, the mobile node managementtable 3217 includes a mobile node IPv4 address 3300 as the IPv4 addressof the mobile node, a foreign IPv4 address 3301 representing the foreignIPv4 address when the home IPv4 mobile agent 3206 transfers the IPv4packet address to the mobile node when this mobile node is moving toanother IPv4 network or to the IPv4/v6 network, and a foreign IPv4mobile agent IPv6 address 3302 representing the IPv6 address of theforeign IPv4 mobile agent. Here, “NULL” is set to the foreign IPv4mobile agent IPv6 address 3302 when the mobile node is moving to theIPv4 network or to the IPv4/v6 network, and the IPv6 address of theforeign IPv4 mobile agent 3208 existing inside the IPv6 network is setwhen the mobile node is moving to this IPv6 network. Incidentally,though this drawing illustrates the case where entries for a pluralityof moving nodes exist, the entry of the mobile node does not exist underthe initial state. The updating processing of this table will be laterdescribed.

FIG. 34 shows an example of the mobile agent address table 3228described above. As shown in this drawing, the mobile agent addresstable 3228 comprises the IPv6 addresses of all the home IPv4 mobileagents existing in the network system (though only the home IPv4 mobileagent 3206 on the LAN-c 3200 is shown in this embodiment), the home IPv4mobile agent IPv6 address 3400 as the IPv4 address and the home IPv4mobile agent IPv4 address 3401. This table is set by a manager, etc.

FIG. 35 shows an example of the movement assistance management table3229 described above. As shown in this drawing, the movement assistancemanagement table 3229 includes a mobile node IPv4 address 3500 as theIPv4 address of the IPv4/v6 mobile node 1806, a home IPv4 mobile agentIPv6 address 3501 as the IPv6 address of the home IPv4 mobile agent 3206existing inside the home network of the mobile node, and a registrationflag 3502 representing whether the entry is “tentative registration” or“real registration”. Though this drawing illustrates the case whereentries for a plurality of mobile nodes exist, the entry for the mobilenode does not exist in this table under the initial state. The updatingprocessing of this table will be described later.

In the construction described above, the processing operations of theIPv4/v6 mobile node 1806, the home IPv4 mobile agent 3206 and theforeign IPv4 mobile agent 3208, and handling of each table describedabove, when the IPv4/v6 mobile node 1806 has moved from the LAN-c 3200as the IPv4/v6 network to the LAN-d 3201 as the IPv6 network, will beexplained in detail.

FIG. 36 is a flowchart showing an example of the processing of the IPv4movement assistance processing portion 3216 for executing the assistanceprocessing of the IPv4 mobile node (not particularly shown in thedrawing) or the IPv4/v6 mobile node 1806, between the networks.

The IPv4 movement assistance processing portion 3216 first judgeswhether or not the message transmission request message for detectingthe IPv4 movement is received (Step 3601). When this message is foundreceived as a result of this judgement (Step 3601YES), the IPv4 movementassistance processing portion 3216 transmits the IPv4 movement detectionmessage (Step 3602). Next, the IPv4 movement assistance processingportion 3216 judges whether or not the IPv4 movement registrationrequest message is received (Step 3603). Here, FIG. 42 shows thestructure of this IPv4 movement registration request message 4200. Asshown in the drawing, the IPv4 movement registration request message4200 includes an IPv4 header 1401 and an IPv4 data 4201. The IPv4 header1401 includes a foreign IPv4 address 1402 and a home IPv4 address 1403,and the IPv4 address of the home IPv4 mobile agent 3206 is set to theforeign IPv4 address 1402 while the IPv4 address of the IPv4/v6 mobilenode 1806 is set to the home IPv4 address 1403. The IPv4 data 4201includes the IPv4 address 4202 as own IPv4 address of the nodetransmitting this message and the foreign IPv4 address 4203 as theforeign address when the IPv4 packet address to this mobile agent istransferred. The same address as the IPv4 address 4202 is set to theforeign IPv4 address 4203 when the IPv4/v6 mobile node 1806 returns tothe LAN-c 3200 as the home network. Incidentally, this message istransmitted by the IPv4 movement processing portion 1813 inside theIPv4/v6 mobile node 1806 explained already with reference to FIG. 22.

When the IPv4 movement registration request message 4200 is foundreceived as a result of judgement (Step 3603YES), the IPv4 movementassistance processing portion 3216 further judges whether or not thismovement registration request is acceptable (Step 3604). When it foundunacceptable as a result of this judgement (Step 3604NO), the IPv4movement assistance processing portion 3216 transmits an IPv4 movementregistration rejection message as a rejection reply message to the IPv4movement registration request message 4200 to the mobile node (Step3605). If it is found acceptable (Step 3604YES), the IPv4 movementassistance processing 3600 then compares its own address 4202 inside themessage with the foreign IPv4 address 4203 (Step 3606).

If own IPv4 address 4202 and the foreign IPv4 address 4203 are found thesame as a result of the judgement described above (Step 3606YES), theIPv4 movement assistance processing portion 3216 judges that the mobilenode has returned to the home network and detects the information of thecorresponding mobile node inside the mobile node management table 3217(Step 3607). The IPv4 movement assistance processing portion 3216transmits the IPv4 movement registration permission message as thepermission reply message of registration of the IPv4 movementregistration request message 4200 to the mobile node (Step 3611).

If own IPv4 address 4202 and the foreign IPv4 address 4203 are founddifferent as a result of the judgement (Step 3609NO), the IPv4 movementassistance processing portion 3216 further judges whether or not theIPv4 movement registration request message 4200 received is the messagewhich is encapsulated by IPv6 encapsulation and transmitted by theforeign IPv4 mobile agent 3208 (Step 3608). Incidentally, this IPv6encapsulation of the IPv4 movement registration request message 4200 bythe foreign IPv4 mobile agent 3208 is executed by the foreign IPv4movement assistance processing portion 3223 inside the later-appearingIPv4 mobile agent 3208. Receiving this IPv4 movement registrationrequest message 4200 which is IPv6 encapsulated in this way, the homeIPv4 mobile agent 3206 decapsulates the message by IPv6 decapsulation byits IPv6 processing portion 3220 and delivers the message to the IPv4movement assistance processing portion 3216. IPv6 decapsulation by thisIPv6 processing portion is one of the services offered by the existingIPv6.

If the result of the judgement represents that the message is not IPv6encapsulated and is not transferred (Step 3608NO), the IPv4 movementassistance processing portion 3216 judges that the mobile node has movedto another IPv4 network or to the IPv4/v6 network and sets theinformation of this mobile node to the mobile node management table3217. (Step 3609). At this time, the value of the foreign IPv4 address4203 inside the received IPv4 movement registration request message 4200is set to the foreign IPv4 address 3301 inside the mobile nodemanagement table 3217 and “NULL” is set to the foreign IPv4 mobile agentIPv6 address 3302. Then, the IPv4 movement assistance processing portion3216 transmits the IPv4 movement registration permission message to themobile node (Step 3611).

If the message is found the one that is IPv6 encapsulated and istransferred as a result of the judgement (Step 3608YES), the IPv4movement assistance processing portion 3216 judges that the mobile nodehas moved to the IPv6 network and sets the information of this mobilenode to the mobile node management table 3217 (Step 3610). At this time,the value of the foreign IPv4 address 4203 inside the transferred IPv4movement registration request message 3300 is set to the foreign IPv4address 3301 inside the mobile node management table 3217, and the valueof the home IPv6 address inside the IPv6 added to the transferred IPv4movement registration request message 4200 is set to the foreign IPv4mobile agent IPv6 address 3302. The IPv4 movement assistance processingportion 3216 encapsulates and transmits the IPv4 movement registrationpermission message as the reply to the mobile node (Step 3612).

The data structure of the IPv6 encapsulated IPv4 movement registrationpermission message 4301 at this time is shown in FIG. 43. As shown inthe drawing, this message has the construction in which the IPv6 header1701 is added to the IPv4 movement registration permission message 4301.The foreign IPv4 mobile agent IPv6 address 3302 registered to the mobilenode management table 3217 is set to the foreign IPv6 address 1702inside the IPv6 header 1701 and own IPv6 address of the home IPv4 mobileagent 3206 itself is set to the home IPv6 address 3003.

The IPv4 movement assistance processing portion 3216 completes theprocessing and thereafter repeats the processing described above.

FIG. 37 is a flowchart showing an example of the processing of theforeign IPv4 movement assistance processing portion 3223 for executingthe movement assistance processing of the IPv4/v6 mobile node 1806between the networks in the foreign IPv4 mobile agent 3208.

The foreign IPv4 movement assistance processing portion 3223 firstjudges whether or not the message transmission request message fordetecting the IPv4 movement is judged (Step 3701). If this message isfound received as a result of this judgement (Step 3701YES), the foreignIPv4 movement assistance processing portion 3223 transmits the IPv4movement detection message (Step 3702). Next, the foreign IPv4 movementassistance processing portion 3223 judges whether or not the IPv4movement registration request message 4200 is received (Step 3703). Ifthis message is found received as a result of the judgement (Step3703YES), the foreign IPv4 movement assistance processing portion 3223tentatively registers the information of this mobile node to themovement assistance management table 3229 (Step 3704). At this time, thevalue of own IPv4 address 4202 inside the received IPv4 movementregistration request message 4200 is set to the foreign IPv4 address3500 inside the mobile node management table 3229 and the value of thehome IPv4 mobile agent IPv6 address 3400, that corresponds to theforeign IPv4 address 1402 inside the IPv4 movement registration requestmessage 4200, is set to the home IPv4 mobile agent IPv6 address 3501 bylooking up the mobile agent address table 3228. Further, “tentativeregistration” is set to the registration flag 3502. The foreign IPv4movement assistance processing portion 3223 encapsulates by IPv6encapsulation the IPv4 movement registration request message 4200 soreceived, and transfers the message to the home IPv4 mobile agent 3206(Step 3705).

The structure of the IPv6 encapsulated IPv4 movement registrationrequest message 4200 at this time is shown in FIG. 44. As shown in thisdrawing, the message 4400 has the construction in which the IPv6 header1701 is added to the IPv4 movement registration permission message 4200shown in FIG. 42. The home IPv4 mobile agent IPv6 address 3501registered to the movement assistance management table 3229 is set tothe foreign IPv6 address 1702 inside the IPv6 header 1701, and own IPv6address of the foreign IPv4 mobile agent 3208 is set to the home IPv6address 1703.

Incidentally, the IPv4/v6 mobile node 1806 always transmits after itsmovement the packet to the foreign IPv4 mobile agent 3208 in accordancewith the processing procedure of the Mobile IPv4. Therefore, the foreignIPv4 mobile agent 3208 can receive the IPv4 movement registrationrequest message 4200.

The foreign IPv4 movement assistance processing portion 3223 sets thetimer (Step 3706) and waits for the IPv4 movement registrationpermission message 4301 as the reply to the IPv4 movement registrationrequest message 4200 for a predetermined time (Steps 3707 and 3710). Bythe way, this IPv4 movement registration permission message 4301 isencapsulated to the IPv6 encapsulated message and is transmitted by thehome IPv4 mobile agent 3206 as described above.

If the IPv4 movement registration permission message 4301 is receivedwithin the predetermined time (Step 3707YES), the foreign IPv4 movementassistance processing portion 3223 updates the registration flag 3502corresponding to the mobile node, which has been tentatively registeredto the mobile agent management table 3229 previously, to “realregistration” (Step 3708). Further, the foreign IPv4 movement assistanceprocessing portion 3223 decapsulates by IPv6 decapsulation the IPv6header 1701 added to the received IPv4 movement registration permissionmessage 4301 and transfers the message to the IPv4/v6 mobile node 1806(Step 3709). If the IPv4 movement registration permission message 4301is not received within the predetermined time (Step 3701YES), theforeign IPv4 movement assistance processing portion 3223 deletes theinformation of this mobile node from the movement assistance managementtable 3229 (Step 3711).

The foreign IPv4 movement assistance processing portion 3223 completesthe processing and thereafter repeats the processing described above.

FIG. 38 is a flowchart showing an example of the processing of thetransfer-to-foreign IPv4 mobile agent processing portion 3219 whichexecutes the processing for transferring the IPv4 packet transmitted byother IPv4 node to the IPv4 mobile node (not particularly shown in thedrawing) or to the IPv4/v6 mobile agent 1806 to the foreign IPv4 mobileagent 3208 existing in the foreign network of the mobile node, in thehome IPv4 mobile agent 3206.

The transfer-to-foreign IPv4 mobile agent processing portion 3219 firstjudges whether or not the IPv4 packet addressed to the mobile noderegistered to the mobile node management table 3217 among the IPv4packets transmitted by the IPv4 node 1804 and other IPv4 nodes (notparticularly shown in the drawing) is received (Step 3801). If thecorresponding packet is found received as a result of this judgement(Step 3801YES), the transfer-to-foreign IPv4 mobile agent processingportion 3219 then judges whether or not the foreign IPv4 mobile agentIPv6 address 3302 of the corresponding mobile node inside the mobilenode management table 3217 is “NULL” (Step 3802). If the foreign IPv4mobile agent IPv6 address 3302 is found “NULL” as a result of thejudgement (Step 3802NO), the transfer-to-foreign IPv4 mobile agentprocessing portion 3219 judges that the mobile node is moving to theIPv4 network or to the IPv4/v6 network, and encapsulates the IPv4 packetso received by IPv4 encapsulation and transmits the encapsulated packet(Step 3804). Incidentally, the processing procedure for effecting IPv4encapsulation and transferring the packet follows the ordinary MobileIPv4.

If the foreign IPv4 mobile agent IPv6 address 3302 is found to be otherthan “NULL” as a result of the judgement (Step 3802YES), thetransfer-to-foreign IPv4 mobile agent processing portion 3219 judgesthat the mobile node is moving to the IPv6 network, encapsulates thereceived IPv4 packet by IPv6 encapsulation and transmits theencapsulated packet to the foreign IPv4 mobile agent 3208 (Step 3803).

The structure of the IPv6 encapsulated IPv4 packet at this time is shownin FIG. 45. This packet has the construction in which the IPv6 header1701 is added afresh to the IPv4 packet 4501. The value of the foreignIPv4 mobile agent IPv6 address 3302 inside the mobile node managementtable 3217 is set to the foreign IPv6 address 1702 inside the IPv6header 1701, and own IPv6 address of the home IPv4 mobile agent 3206 isset to the home IPv6 address 1703.

The transfer-to-foreign IPv4 mobile agent processing portion 3219completes the processing and thereafter executes repeatedly theprocessing described above.

FIG. 39 is a flowchart showing an example of the processing of thetransfer-to-other node processing portion 3221 which executes theprocessing for transferring the packet to the IPv4 node when the IPv4packet transmitted by the IPv4/v6 mobile node 1806 to other IPv4 node onthe foreign IPv6 network is encapsulated by IPv6 encapsulation andtransferred by the foreign IPv4 mobile agent 3208, in the home IPv4mobile agent 3206.

The transfer-to-other node processing portion 3221 first judges whetheror not the IPv6 packet address to the home IPv4 mobile agent 3208 itselfis received (Step 3901). If the packet is found received as a result ofthis judgement (Step 3901YES), the transfer-to-other node processingportion 3221 then judges whether or not the packet is the IPv4 packetthat is encapsulated and transferred by the foreign IPv4 mobile agent3208 (Step 3902). Incidentally, this transfer of the IPv4 packet by theforeign IPv4 mobile agent 3208 is executed by the transfer-to-IPv4mobile agent processing portion 3225 inside the later-appearing foreignIPv4 mobile agent 3208. If the packet is not found the transferred IPv4packet as a result of the judgement (Step 3902NO), the transfer-to-othernode processing portion 3221 discards this packet (Step 3905). If it isfound the transferred IPv4 packet (Step 3902YES), the transfer-to-othernode processing portion 3221 further judges whether or not the foreignnode of this IPv4 packet is the mobile node registered to the mobilenode management table 3217 (Step 3903). If it is not found registered asa result of the judgement (Step 3903NO), the transfer-to-other nodeprocessing portion 3221 discards this packet (Step 3905). If it is foundregistered (Step 3903YES), the transfer-to-other node processing portion3221 decapsulates this packet by IPv6 decapsulation and transmits it tothe foreign IPv4 node (Step 3904).

The transfer-to-other node processing portion 3221 completes theprocessing and thereafter repeats the processing described above.

FIG. 40 is a flowchart showing an example of the processing of thetransfer-to-home IPv4 mobile agent processing portion 3225 whichexecutes the processing for transferring the IPv4 packet, which theIPv4/v6 mobile node 1806 transmits to other IPv4 nodes, to the home IPv4mobile agent 3206 in the foreign IPv4 mobile agent 3208.

The transfer-to-home IPv4 mobile agent processing portion 3225 firstjudges whether or not the IPv4 packet, which is registered to themovement assistance management table 3229 and is transmitted by theIPv4/v6 mobile agent 1806, is received (Step 4001). If the correspondingpacket is found received as a result of this judgement (Step 4001YES),the transfer-to-home IPv4 mobile agent processing portion 3225 thenjudges whether or not the registration flag 3502 of the correspondingmobile node inside the mobile node management table 3229 is “realregistration” (Step 4002). If the registration flag is found the “realregistration” as a result of the judgement (Step 4002YES), thetransfer-to-home IPv4 mobile agent processing portion 3225 encapsulatesthe received IPv4 packet by IPv6 encapsulation and transmits it to thehome IPv4 mobile agent 3206 (Step 4003).

The IPv4 packet subjected to IPv6 encapsulation at this time has thesame structure as the structure shown already in FIG. 45. The value ofthe corresponding home IPv4 mobile agent IPv6 address 3501 inside themovement assistance management table 3229 is set to the foreign IPv6address inside the IPv6 header 1701 and the IPv6 address of the foreignIPv4 mobile agent 3208 itself is set to the foreign IPv6 address 1703.

If the registration flag 3502 is not found the “real registration” as aresult of the judgement (Step 4002NO), the transfer-to-home IPv4 mobileagent processing portion 3225 discards this packet (Step 4004). Thetransfer-to-home IPv4 mobile agent processing portion 3225 completes theprocessing and thereafter repeats the processing described above.

FIG. 41 is a flowchart showing an example of the processing of thetransfer-to-other mobile node processing portion 3227 which executes theprocessing for transferring the packet to the IPv4/v6 mobile node 1806when the IPv4 packet transmitted by other IPv4 node to the IPv4/v6mobile node 1806 by the home IPv4 mobile agent 3206 is encapsulated byIPv6 encapsulation and is transferred, in the foreign IPv4 mobile agent3208.

The transfer-to-mobile node processing portion 3227 first judges whetheror not the IPv6 packet addressed to the foreign IPv4 mobile agent 3208itself is received (Step 4101). If it is found received as a result ofthis judgement (Step 4101YES), the transfer-to-mobile node processingportion 3227 then judges whether or not the received packet is the IPv4packet which is IPv6 encapsulated and transferred by the home IPv4mobile agent 3206 (Step 4102). Incidentally, this transfer of the IPv4packet by the home IPv4 mobile agent 3206 is executed by the home IPv4movement assistance processing portion 3219 described above. If thepacket is not the transferred IPv4 packet as a result of the judgement(Step 4102NO), the transfer-to-mobile node processing portion 3227discards this packet (Step 4105). If it is the transferred IPv4 packet(Step 4102YES), the transfer-to-mobile node processing portion 3227further judges whether or not the node of this IPv4 packet is the mobilenode registered really to the movement assistance management table 3229(Step 4103). If the node is not found registered really (Step 4103NO) asa result of this judgement, the transfer-to-mobile node processingportion 3227 discards the packet (Step 4105). If it is found registeredreally (Step 4103YES), the transfer-to-mobile node processing portion3227 decapsulates this packet by IPv6 decapsulation and transfers thepacket to the IPv4/v6 mobile agent 1806 (Step 4104).

The transfer-to-other node processing is completed and thereafter theprocessing described above is repeatedly executed.

The flow of the processings shown in FIG. 22 and in FIGS. 36 to 41 willbe explained with reference to the network system shown in FIG. 32. Whenthe IPv4/v6 mobile node 1806 exists on the LAN-c 3200 as the homenetwork, the IPv4/v6 mobile node 1806 is judged as not moving because itreceives the IPv4 movement detection message and the IPv6 movementdetection message transmitted by the home IPv4 mobile agent 3206 and theIPv6 mobile agent-c 3207, respectively.

When the IPv4/v6 mobile node 1806 has moved to the LAN-d 3201, theIPv4/v6 mobile node 1806 is judged as having moved to another networkbecause it receives the IPv4 movement detection message and the IPv6movement detection message transmitted by the foreign IPv4 mobile agent3208 and the IPv6 mobile agent-d 3209, respectively. Then, the IPv4/v6mobile node transmits the IPv4 movement registration request message4200 and the IPv6 movement registration request message 3000 by means ofthe IPv4 movement processing portion 1813 and the IPv6 movementprocessing portion 1815 to the home IPv4 mobile agent 3206 and to theIPv6 mobile agent-c 3207, respectively.

To this IPv4 movement registration request message 4200 are set“10.0.0.1” (home IPv4 mobile agent 3206) as the foreign IPv4 address1402, “10.0.0.30” as its own IPv4 address 3202 and “20.0.0.30” (as theforeign IPv4 address which the IPv4/v6 mobile node 1806 acquires fromthe foreign IPv4 mobile agent 3208 in the foreign LAN-d 3201 in thisembodiment), as the transfer IPv4 address.

In this embodiment, the IPv4 packet cannot come out from the LAN-d 3201beyond the router to the external network as described above but cantransmit/receive the IPv4 packet inside the LAN-d 3201. Therefore, theIPv4/v6 mobile node 1806 can receive the IPv4 movement detection messagetransmitted by the foreign IPv4 mobile agent 3208 and can also transmitthe IPv4 movement registration request message 4200 to the LAN-d 3201.

This IPv4 movement registration request message 4200 is once received bythe foreign IPv4 mobile agent 3208. The foreign IPv4 mobile agent 3208adds the IPv6 header 1701, in which “11::1” (home IPv4 mobile agent3206) is set as the foreign IPv6 address 1702 and “21::1” (foreign IPv4mobile agent 3208) is set as the home IPv6 address 1703, to this message4200 by means of its foreign IPv4 movement assistance processing portion3223, and transfers the message to the home IPv4 mobile agent 3206.Thereafter, this message is received by the home IPv4 mobile agent 3206.After receiving this message, the home IPv4 mobile agent 3206 adds theIPv6 header 1701, in which “21::1” (foreign IPv4 mobile agent 3206) isset as the foreign IPv6 address 1702) and “11::1” (home IPv4 mobileagent 3208) is set as the home IPv6 address 1703, to the IPv4 movementregistration permission message 4301 by means of its IPv4 movementassistance processing portion 3216, and transfers the message to theforeign IPv4 mobile agent 3208. Receiving this message, the foreign IPv4mobile agent 3208 decapsulates the message by IPv6 decapsulation by itsforeign IPv4 movement assistance processing portion 3223 and transmitsthe message to the IPv4/v6 mobile node 1806.

In this way, registration of the movement of the IPv4/v6 mobile node1806 to the home IPv4 mobile agent 3206 is completed. At this time,“10.0.0.30” is set as the information of the IPv4/v6 mobile node 1806 tothe mobile node IPv4 address 3300 of the mobile node management table3217, “20.0.0.30” is set to the foreign IPv4 address 3301 and “21::1” isset to the foreign IPv4 mobile agent IPv6 address 3302. Further,“10.0.0.30” is set to the mobile node IPv4 address 3500 of the movementassistance management table 3229 and “11::1” is set to the foreign IPv4mobile agent IPv6 address 3501.

Receiving the IPv4 packet transmitted from the IPv4 node 3203 to theIPv4/v6 mobile node 1806, the home IPv4 mobile agent 3206 adds theheader 1701, in which “21::1” (foreign IPv4 mobile agent 3208) is set tothe foreign IPv6 address 1702 and “11::1” (home IPv4 mobile agent 3206)is set to the home IPv6 address 1703, to the IPv4 packet by means of thetransfer-to-foreign IPv4 mobile agent processing portion 3219, andtransfers the packet to the foreign IPv4 mobile agent 3208. The IPv6encapsulated packet is received by the foreign IPv4 mobile agent 3208.The foreign IPv4 mobile agent 3208 decapsulates this packet by IPv6decapsulation by its transfer-to-node processing portion 3227 andtransmits it to the IPv4/v6 mobile node 1806. The IPv4/v6 mobile node1806 receives and processes this packet as the IPv4 packet in accordancewith the procedure of the ordinary Mobile IPv4.

When the IPv4/v6 mobile node 106 receives the IPv4 packet transmitted tothe IPv4 node 3203, on the contrary, the foreign IPv4 mobile agent 3208adds the IPv6 header 1701, in which “11::1” (home IPv4 mobile agent3206) is set to the foreign IPv6 address 1702 and “21::1” (foreign IPv4mobile agent 3208) is set to the home IPv6 address 1703, to the packetby means of the transfer-to-home IPv4 mobile agent processing portion3205 and transmits the packet to the home IPv4 mobile agent 3206. TheIPv6 encapsulated packet is received by the home IPv4 mobile agent 3206.The home IPv4 mobile agent 3206 decapsulates this packet by IPv6decapsulation by its transfer-to-other node processing portion 3221 andthen transmits it to the foreign IPv4 node 3203. The IPv4 node 3203receives and processes this packet as the ordinary IPv4 packet.

According to the present invention described above, even when theIPv4/v6 mobile node 1806 moves from the LAN-c 3200 as the IPv4/v6network to the LAN-d 3201 as the IPv6 network, the IPv4/v6 mobile node1806 can receive the IPv4 packet transmitted by the IPv4 node 3203 tothe IPv4/v6 mobile node 1806. On the contrary, the existing IPv4 node3203 can receive the IPv4 packet transmitted by the IPv4/v6 mobile node1806 to the IPv4 node 3203.

Communication by making use of the IPv6 between other node and theIPv4/v6 mobile node 1806 can be made by the assistance of movement bythe IPv6 mobile agent-c 3207 supporting the IPv6 and by the assistanceof movement of the node in the IPv6 by the IPv6 mobile agent-d 3209.

Incidentally, when the IPv4/v6 mobile node 1806 returns from the LAN-d3201 to the LAN-c 3200, the IPv4/v6 mobile node 1806 detects its returnto the home network by the IPv4 movement processing 1813 describedalready. Then, the IPv4/v6 mobile node 1806 transmits the IPv4 movementregistration request message, in which “10.0.0.30” is set to its ownaddress 4202 and “10.0.0.30” having the same address as its own IPv4address 4202 to the foreign IPv4 address 4203, to the home IPv4 mobileagent 3206. Receiving this IPv4 movement registration request message4200, the home IPv4 mobile agent 3206 judges that the IPv4/v6 mobilenode 1806 has returned to the LAN-c 3200 as the home network because itsown IPv4 address 4202 in the message has the same address as that of theforeign IPv4 address 4203, and then deletes the information of thismobile node in the mobile node management table 3217. As a result, theIPv4/v6 mobile node 1806 can make communication by utilizing theordinary IPv4. Similarly, the IPv4/v6 mobile node 1806 reports thereturn to the LAN-c 3200 by the IPv6 movement registration requestmessage 3000 to the IPv6 mobile agent-c 3207, too, in accordance withthe processing procedure of the Mobile IPv6. Therefore, communicationutilizing the ordinary IPv6 can be made, as well.

1-19. (canceled)
 20. A mobile apparatus for performing communicationswith another apparatus connected to a network by using a first typeinternet protocol and a second type internet protocol, comprising: acommunication portion for transmitting/receiving a packet to/from anetwork, the packet being compliant with the first type internetprotocol or the second type internet protocol; a movement detectionprocessing portion that, when the mobile apparatus is moved from a firstnetwork to a second network, executes judgment as to whether the secondnetwork is a network in which communications are performed by using atleast the first type internet protocol or a network in whichcommunications are performed by using the second type internet protocol;and a packet transmission portion that, when a first packet compliantwith the first type internet protocol is to be transmitted to anotherapparatus connected to a network, creates a second packet by executingencapsulation for encapsulating the first packet with the second typeinternet protocol, and transmits the second packet via the communicationportion, if the movement detection processing portion executes judgmentthat the second network is a network in which communications areperformed by using the second type internet protocol.
 21. The mobileapparatus according to claim 20, wherein the movement detectionprocessing portion executes, when the mobile apparatus is moved from thefirst network to the second network, the judgment based on whether anetwork address acquired as an after-movement network address of thesecond network corresponds to the first type internet protocol or thesecond type internet protocol.
 22. The mobile apparatus according toclaim 20, further comprising a movement state storing portion thatstores the network address of the second network as an after-movementnetwork address, when the mobile apparatus is moved from the firstnetwork to the second network, wherein the movement state storingportion further stores; a network address corresponding to the firsttype internet protocol of the second network, if the second network is anetwork in which communications are performed by using the first typeinternet protocol, a network address corresponding to the second typeinternet protocol of the second network, if the second network is anetwork in which communications are performed by using the second typeinternet protocol; and network addresses corresponding to the first andsecond internet protocols of the second network, if the second networkis a network in which communications are performed by using the firstand second internet protocols.
 23. The mobile apparatus according toclaim 20, wherein the packet transmission portion executes theencapsulation by adding a header corresponding to the second typeinternet protocol to the first packet, the header including, as adestination address, an address of a mobile agent connected to the firstnetwork, for assisting movement of the mobile apparatus and, as a sourceaddress, an address corresponding to the second type internet protocolacquired in the second network by the mobile apparatus.
 24. The mobileapparatus according to claim 20, wherein the packet transmission portiontransmits the first packet via the communication portion, if themovement detection processing portion executes judgment that the secondnetwork is a network in which communications are performed by using thefirst type internet protocol.
 25. The mobile apparatus according toclaim 20, further comprising a movement registration portion that, ifthe movement detection processing portion executes judgment that thesecond network is a network in which communications are performed byusing the second type internet protocol, acquires a first IP addresscompliant with the second type internet protocol and to be used in thesecond network, creates a registration request message requestinganother mobile agent connected to the first network to register thefirst IP address, and transmits the registration request message via thecommunication portion by encapsulating the registration request messagewith a message compliant with the second type internet protocol.
 26. Amobile apparatus for performing communications with another apparatusconnected to a network by using a first type internet protocol and asecond type internet protocol, comprising: a communication portion fortransmitting/receiving a packet to/from the network, the packet beingcompliant with the first type internet protocol or the second typeinternet protocol; a movement detection processing portion that, whenthe mobile apparatus is moved from a first network to a second network,executes judgment as to whether the second network is a network in whichcommunications are performed by using at least the first type internetprotocol or a network in which communications are performed by using thesecond type internet protocol; and a packet transmission portion that,when a first packet compliant with the first type internet protocol isto be transmitted to another apparatus connected to a network, creates,if the movement detection processing portion executes judgment that thesecond network is a network in which communications are performed byusing the second type internet protocol, a second packet by adding aheader to the first packet, and transmits the second packet via thecommunication portion, the header including, as a destination address, afirst address compliant with the second type internet protocol of amobile agent connected to the first network, for assisting movement ofthe mobile apparatus and, as a source address, a second addresscompliant with the second type internet protocol acquired in the secondnetwork by the mobile apparatus.
 27. A mobile apparatus including acommunication portion for transmitting/receiving a packet to/from anetwork, the packet being compliant with a first type internet protocolor a second type internet protocol, the mobile apparatus for performingcommunications with another apparatus connected to a network by usingthe first type internet protocol and the second type internet protocol,comprising: a movement state storing portion that, when the mobileapparatus is moved from a first network to a second network, stores anetwork address of the second network as an after-movement networkaddress; and a packet transmission portion that, when a first packetcompliant with the first type internet protocol is to be transmitted toanother apparatus connected to a network, judges whether the secondnetwork is a network in which communications are performed by using atleast the first type internet protocol or a network in whichcommunications are performed by using the second type internet protocolbased on contents of the after-movement network address stored in themovement state storing portion, and, if the second network is a networkin which communications are performed by using the second type internetprotocol, creates a second packet by encapsulating the first packet witha packet compliant with the second type internet protocol to transmitthe second packet via the communication portion.
 28. The mobileapparatus according to claim 27, wherein the movement state storingportion stores at least one network address compliant with the first andsecond type internet protocols of the second network.
 29. The mobileapparatus according to claim 27 wherein: the movement state storingportion stores a network address compliant with the first type internetprotocol if the second network is a network in which communications areperformed by using the first type internet protocol, or a networkaddress compliant with the second type internet protocol if the secondnetwork is a network in which communications are performed by using thesecond type internet protocol, and the movement state storing portionstores network addresses compliant with the first and second typeinternet protocols if the second network is a network in whichcommunications are performed by using the first and second type internetprotocols of the second network.
 30. A mobile apparatus including acommunication portion for transmitting/receiving a packet to/from anetwork, the packet being compliant with a first type internet protocolor a second type internet protocol, the mobile apparatus for performingcommunications with another apparatus connected to a network by usingthe internet protocol, comprising: a movement state storing portionthat, when the mobile apparatus is moved from a first network to asecond network, stores a network address of the second network as anafter-movement network address; a creation portion that creates a firstpacket compliant with the first type internet protocol to be sent toanother apparatus connected to a network; and a packet transmissionportion that judges, from the after-movement network address stored inthe movement state storing portion, whether the second network is anetwork in which communications are performed by using at least thefirst type internet protocol or a network in which communications areperformed by using the second type internet protocol; creates, if thesecond network is a network in which communications are performed byusing the second type internet protocol, a second packet by adding aheader to the first packet, the header including, as a destinationaddress, a first address compliant with the second type internetprotocol of a mobile agent connected to the first network, for assistingmovement of the mobile apparatus and, as a source address, a secondaddress compliant with the second type internet protocol acquired in thesecond network by the mobile apparatus; and transmits the second packetvia the communication apparatus.
 31. A mobile apparatus including acommunication portion for transmitting/receiving a message to/from anetwork, a first processing portion for performing a process compliantwith a first type internet protocol, and a second processing portion forperforming a process compliant with a second type internet protocol, themobile apparatus performing communications with another apparatusconnected to a network by using the first type internet protocol and asecond type internet protocol, comprising: a movement detection portionthat, when the mobile apparatus is moved from a first network in whichcommunications are performed by using at least the first type internetprotocol to a second network in which communications are performed byusing the second type internet protocol, receives a first messagecompliant with the second type internet protocol via the communicationportion from a first mobile agent connected to the second network, anddetects, based on information contained in the first message, that themobile apparatus has moved from the first network to the second network;and a movement registration portion that acquires a first IP addresscompliant with the second type internet protocol and to be used in thesecond network, creates a second message compliant with the first typeinternet protocol, the second message requesting a second mobile agentconnected to the first network to register the first IP address, createsa third message by encapsulating the second message with a messagecompliant with the second type internet protocol, and transmits thethird message via the communication portion.
 32. The mobile apparatusaccording to claim 31, wherein the second message includes the first IPaddress and a second IP address compliant with the first type internetprotocol of the mobile apparatus.
 33. The mobile apparatus according toclaim 31, wherein the movement registration portion creates the thirdmessage by adding header information compliant to the second typeinternet protocol to the second message, the header informationincluding, as a destination address, a second IP address compliant withthe second type internet protocol of the second mobile agent, and thefirst IP address as a source address.
 34. The mobile apparatus accordingto claim 30, wherein the movement registration portion receives a fourthmessage including the first IP address as a destination address via thecommunication portion, the fourth message being sent from the secondmobile agent in response to the third message, and created byencapsulating a response message compliant with the first type internetprotocol with a message compliant with the second type internetprotocol.
 35. The mobile apparatus according to claim 34, wherein thefourth message is created by adding header information to the responsemessage including a second IP address as a source address, the second IPaddress being an address of the second mobile agent and compliant withthe second type internet protocol, and the header information beingcompliant with the second type internet protocol and including the firstIP address as a destination address.
 36. The mobile apparatus accordingto claim 34, wherein the movement registration portion decapsulates thefourth message received into the response message.
 37. The mobileapparatus according to claim 31, wherein, when the mobile apparatusreturned to the first network from the second network, the movementdetection portion receives a fourth message compliant with the firsttype internet protocol from the second mobile agent via thecommunication portion; and detects, based on information contained inthe fourth message, that the mobile apparatus has moved to the firstnetwork; and the movement registration portion creates a fifth messagecompliant with the first type internet protocol and requesting thesecond mobile agent to register a second IP address of the mobileapparatus, the second IP address being compliant with the first typeinternet protocol, and transmits the fifth message via the communicationportion.
 38. A mobile apparatus including a communication portion fortransmitting/receiving a message to/from a network, a first processingportion for performing a process compliant with a first type internetprotocol, and a second processing portion for performing a processcompliant with a second type internet protocol, the mobile apparatus forperforming communications with another apparatus connected to a networkby using the first type internet protocol and a second type internetprotocol, comprising: a movement detection portion that, when the mobileapparatus is moved to a second network from a first network in whichcommunications are performed by using at least the first type internetprotocol, receives a first message from a first mobile agent connectedto the second network, and detects, based on information contained inthe first message, that the mobile apparatus has moved from the firstnetwork to the second network; and a movement registration portion thatacquires a first IP address to be used in the second network, creates asecond message compliant with the first type internet protocol, thesecond message requesting a second mobile agent connected to the firstnetwork to register the IP address, creates, if the second network is anetwork in which communications are performed by using the second typeinternet protocol, a third message by encapsulating the second messagewith a message compliant with the second type internet protocol, andtransmits the third message via the communication portion.
 39. Themobile apparatus according to claim 38, wherein the movementregistration portion transmits the second message via the communicationportion, if the second network is a network in which communications areperformed by using at least the first type internet protocol.